Essex's Harmer takes five wickets; Cook passes 50
Lancs' Buttler & Hameed out cheaply
Duckett scores 89-ball century
Stokes out for a duck for Durham
Fifties for Surrey's Roy, Burns & Sangakkara
Hampshire 110-2 v Somerset
Another fifty, this time for Liam Dawson. The all-rounder has come in to open the batting for Hampshire in place for Michael Carberry and he's adapted well to the change in role.
He's taken 132 balls, batting patiently to keep the Somerset attack out. James Vince is alongside him, with eight runs to his name.
Yorkshire v Surrey 166-2
Image source, Rex FeaturesRory Burns follows his batting partner to fifty, albeit from many more deliveries. It's taken the left-hander 126 balls to get there.
The partnership with Jason Roy is worth 92 runs and Surrey are on top at Headingley for the time-being.
Glamorgan v Derbyshire 120-2
Nick Webb
BBC Wales Sport
Wayne Madsen went for 70, his highest score of the season, in a lively spell from Timm van der Gugten after the lunch/tea/whatever interval.
Madsen was caught behind fencing at a rising delivery from the Netherlands paceman, who earlier had Luis Reece lbw for one.
The pink ball doesn't appear to be coming very hard off the pitch or bat at the moment, while we've got the lights on already on a gloomy afternoon/evening.
But Derbyshire will be reasonably satisfied with the first half of the day, given their struggles so far this season.
Essex v Middlesex 158-5
Mohammad Amir is the man again! The Pakistan fast bowler has his second wicket - and lbw decision - of the day, pinning John Simpson in front early doors.
After a wonderful partnership between Stevie Eskinazi and Dawid Malan, the momentum has swung back in Essex's favour.
Amir has 2-26.
Image source, Rex FeaturesSussex 135-3 v Gloucestershire
Bob Hunt
BBC Radio Gloucestershire
Luke Wright is beginning to enjoy himself in the post-prandial session at Hove.
He hoisted his very first ball for six, survived a very strong lbw appeal with his third and is on 46 as Sussex aim to increase the tempo after a fairly turgid opening .
David Payne has bowled superbly for Gloucestershire his 12 overs going for just 12 runs.
Yorkshire v Surrey 152-2
Image source, Rex FeaturesJason Roy moves to fifty in his first County Championship outing of the season. He's looked in fine touch, putting his controversial run-out for obstruction in the T20 against South Africa behind him.
It's come in typically brisk fashion - just 54 balls. Yorkshire really need to dismiss him, or he can really hurt them.
Allow Twitter content?
This article contains content provided by Twitter. We ask for your permission before anything is loaded, as they may be using cookies and other technologies. You may want to read Twitter’s cookie policy, external and privacy policy, external before accepting. To view this content choose ‘accept and continue’.
BBC Sport app users may need to click the link to view this tweet.
Notts v Kent 125-6
Dave Bracegirdle
BBC Radio Nottingham commentator
Notts have picked up a second bowling point.
Will Gidman had led a charmed life on his way to making 25 but was then castled by Harry Gurney, who flattened the left-hander's off stump.
Daniel Bell-Drummond is still there, the opener has 55, after reaching his 50 from 99 balls.
Essex v Middlesex 146-4
Jamie Porter in on the act now for Essex, removing Middlesex's second batsman in a few overs.
Stevie Eskinazi the man to go this time, with Alastair Cook pouching the catch at slip. Essex are right back in this, with John Simpson joining Paul Stirling at the crease.
Hmm, interesting point raised by BBC Sport's Stephan Shemilt who's at Edgbaston.
It may become an issue over the next couple of days - I'm sorry to say the forecast for Birmingham is abysmal.
Allow Twitter content?
This article contains content provided by Twitter. We ask for your permission before anything is loaded, as they may be using cookies and other technologies. You may want to read Twitter’s cookie policy, external and privacy policy, external before accepting. To view this content choose ‘accept and continue’.
BBC Sport app users may have to click 'view more' to see this Tweet.
Hampshire 86-2 v Somerset
I told you he was out of form. Rilee Rossouw goes for a rotten 10-ball duck, caught by Steven Davies off a top-edge from Craig Overton's bowling.
A fifth duck in his last eight County Championship innings. His form is a serious worry for Hampshire now, with his early-season runs a distant memory.
Essex v Middlesex 126-3
Image source, Rex FeaturesSimon Harmeris enjoying his cricket at the moment.
The South African off-spinner removes the dangerous, in-form Middlesex skipper Dawid Malan as he edges behind to veteran keeper James Foster.
An important wicket for Essex, with a 124-run partnership with Stevie Eskinazi broken.
Division Two update
Ben Duckett's superb innings for Northants has just been ended by Leicestershire's Rob Sayer.
Duckett struck 21 fours in his 102-ball knock to leave Northants handily placed at 160-3.
Kent opener Daniel Bell-Drummond is resisting the Notts' pace attack and has gone past 50. Kent are 113-5 at Trent Bridge.
Durham have gone past 100, but are seven down against Worcestershire, while Derbyshire's Wayne Madsen has just fallen for 70 at Glamorgan.
Sussex are ticking along nicely on 105-3 against Gloucestershire at Hove.
Essex v Middlesex 120-2
"When does the night bit start Dave?"
Disclaimer: The chaps in this photo may not be called Dave.
Image source, Rex FeaturesWarwickshire v Lancashire 89-4
Important spell at Edgbaston, where Lancashire have key run-getters Shiv Chanderpaul (22 not out) and Dane Vilas (8 not out) in the middle.
Both have been very important to their form so far. If Warwickshire, still looking for a first win of the season, can crack the middle order then they'll fancy their chances.
Hampshire 84-1 v Somerset
Finally, a breakthrough for Somerset. Craig Overton is the man who has struck, having Hampshire opener Jimmy Adams caught by James Hildreth at first slip.
Adams and Liam Dawson made a sedate but solid start, putting on a good opening stand, but out-of-form Rilee Rossouw now comes to the crease.
Yorkshire v Surrey 115-2
Jason Roy and Rory Burns are batting for Surrey and it's fair to say they've taken a different approach so far.
Roy, in his first Championship game of the season, has raced to 28 not out off 33 balls, while Burns has 25 from 94 balls.
Essex v Middlesex 111-2
Image source, Rex FeaturesNo messing about for Middlesex, with Dawid Malan and Stevie Eskinazi both passing their half-centuries straight after the re-start.
Their partnership is worth 109 and with memories of hostile pace and swing fading, the away side will hope to pile on the runs this session.
Every ball covered
Allow Twitter content?
This article contains content provided by Twitter. We ask for your permission before anything is loaded, as they may be using cookies and other technologies. You may want to read Twitter’s cookie policy, external and privacy policy, external before accepting. To view this content choose ‘accept and continue’.
Don't forget, ball-by-ball BBC local radio commentary is available on all nine games.
Click on the links at the top of this page to tune in.
Thanks Gary. It's certainly a tricky debut for the pink ball, forced to walk a tightrope it cannot really win.
With nine games going on there is bound to be examples of batting collapses, good bowling and batting partnerships. If wickets tumble - as they did at Chester-le-Street and Trent Bridge in particular this morning - accusations of a bowler-friendly ball are likely to arise. Similarly, if batsmen make hay while the sun shines then bowlers will complain.
Let us hope for some intriguing, balanced and competitive stuff this session.
Allow Twitter content?
This article contains content provided by Twitter. We ask for your permission before anything is loaded, as they may be using cookies and other technologies. You may want to read Twitter’s cookie policy, external and privacy policy, external before accepting. To view this content choose ‘accept and continue’.
BBC Sport app users may need to click the link to view this tweet.
With a few minutes to go until the players emerge for the second session, I'll hand you over to Felix Keith to take you through the next couple of hours.