Stuart Broad and James Anderson on opposite sides as Notts bowl out Lancashire for 214.
Surrey's Gus Atkinson takes 6-68 - his first five-for - for 2022 champions against Essex.
Second-placed Hampshire all out for 229 on day one against Warwickshire.
Australia batter Steve Smith makes debut for Sussex at New Road
Jonny Bairstow takes three catches behind stumps for Yorkshire against Glamorgan.
On-loan paceman Henry Brookes takes 6-20 on debut for Derbyshire.
Hampshire 83-2 v Warwickshire
Breakthrough for Warwickshire.
The partnership of 74 is over after Nick Gubbins gets an edge trying to defend on the back foot, flashing the ball towards Sam Hain at second sllip.
Hain deflects the ball into the sky off his sternum allowing Rob Yates to take a simple catch.
James Vince comes in but ... hold on.
Notts v Lancs 110-4
A few minutes ago this looked like being Lancashire's morning, but Notts have taken two quick wickets to swing the momentum their way before lunch at Trent Bridge.
Dane Vilas, back captaining Lancashire in the absence of Keaton Jennings, edges to Lyndon James at first slip for a first-ball duck.
Brett Hutton has 2-31 after earlier dismissing Luke Wells.
Essex 92-1 v Surrey
Normal service is resumed for Essex as Alastair Cook strokes Kemar Roach away for four to bring up a 73-ball half-century.
The former England skipper - who was dropped on 13 - now has 120 50s in first-class cricket, to go with his 73 hundreds.
Somerset v Northamptonshire 85-1
Ricardo Vasconcelos despatches three straight deliveries from Lewis Gregory to the fence to move onto 44.
Nine fours this morning. Why run when you can find the ropes, I suppose!?
Craig Overton returns to the attack with an absolute jaffa which narrowly beats the bat, the pad and the stumps on its way through to the keeper. Who needs a loosener?
Derbys v Leics 57-6
Derbyshire strike again as Luis Reece bowls Australian Peter Handscomb for five. The left-armer has 2-7 from five overs. Tom Scriven is the new Leicestershire batter.
Notts v Lancs 109-3
Stuart Broad is back in the Notts attack and has his first wicket of the day.
Broad floats one full and a bit wider, Steven Croft thinks it's Christmas and attempts to smash it through the covers, but can only get a feather of an edge through to wicketkeeper Joe Clarke.
Essex 87-1 v Surrey
Alastair Cook's previous scores so far this season were a very unCook-like 16, 28, 16, 0 and 39.
He progresses to 45 not out with a cover drive off Gus Atkinson for his sixth four of the morning.
Hampshire 77-1 v Warwickshire
A glorious back-foot punch to the rope off Chris Rushworth through point takes Fletcha Middleton to 42.
That's eight fours now. Feels like the reward for negotiating those tough opening 30 minutes when scoring shots were at a premium.
Essex 80-1 v Surrey
Kemar Roach is back in business for Surrey. A decent start to his pre-lunch burst, with just a couple of singles from it. Alastair Cook is 39 not out and Tom Westley has 11.
If you missed it earlier on, Nick Browne was the man to go, caught at slip off Gus Atkinson for 16.
Yorkshire v Glamorgan 46-2
Yorkshire think they've got Marnus Labuschagne caught behind, but bowler Mickey Edwards and his team-mates are disappointed not to see the umpire's finger go up.
It's been slow going from Labuschagne, he's scored 10 off 70 balls, but despite not being the most free-scoring off innings from the Australia batter, Yorkshire will be keen to see the back of him given his undoubted quality.
Somerset v Northamptonshire 65-1
There's the breakthrough. Hassan Azad had been tempted into a couple of injudicious pushes by Kasey Aldridge and third time's a charm.
Azad edges to Craig Overton at third slip and he takes the catch at the second-attempt after a quick juggle.
Having seen Azad put down in the slips off his own bowling in the first over, Overton will be delighted, I'm sure.
Sam Whiteman, skipper for this game, is in at three.
Worcs 75-5 v Sussex
Fynn Hudson-Prentice finds a bit of late inswing, but the line isn't quite right and Adam Hose is able to adjust and flick it away for four.
Worcestershire need a substantial partnership to steady this innings and Hose is now 21 not out, with Gareth Roderick on 11.
Hampshire 64-1 v Warwickshire
Danny Briggs has been brought on by the visitors. Anything to disrupt the flow of this nice little partnership forming between Fletcha Middleton and Nick Gubbins.
Middleton leaves an arm-ball from the left-armer but it drifts agonisingly close to the timbers.
Fascinating period of play at the Ageas, and we are less than 90 minutes into day one. Chris Rushworth has returned for a second spell from the other end as the visitors seek a breakthrough.
Somerset v Northants 61-0
Andrew Radd
BBC Radio Northampton commentator
So far, so good for Northamptonshire after being put in to bat on a green-looking pitch with Ricardo Vasconcelos and Hassan Azad sharing the county's first half-century opening stand of the season.
It's welcome good news for the visitors who have made five changes to the side hammered by Hampshire last time out, including Sam Whiteman - captain of Western Australia - taking charge of the team for the first time with Luke Procter ruled out through a shoulder injury.
Jordan Buckingham, the highly-rated young Australian fast bowler, becomes Northamptonshire's 541st first-class cricketer and will stay with the club for the next three Championship matches.
Notts v Lancs 94-2
A half-century off 49 balls for Josh Bohannon, including eight boundaries.
It's the third time that he has passed 50 in six innings for Lancashire this season.
Somerset v Northamptonshire 61-0
That brief delay to proceedings hasn't messed with his timing... a b-e-a-utiful cover drive from Ricardo Vasconcelos there to move to 32.
Derbys v Leics 49-5
Image source, Rex FeaturesHenry Brookes is having quite a debut for Derbyshire and takes two wickets in an over for the second time
First he has Colin Ackermann caught at slip and then Wiaan Mulder departs after edging to the keeper.
Leicestershire have also lost Rishi Patel, bowled by all-rounder Luis Reece for 11, with the ball just clipping the top of off stump as he pushed forward in defence.
Brookes now has the amazing figures of 4-1. What can England's Rehan Ahmed do about this situation?
Somerset v Northamptonshire 53-0
Short and sharp indeed. We're back under way.
Worcs 65-5 v Sussex
Four Sussex slips in place as Fynn Hudson-Prentice strays onto Adam Hose's pads and the Worcestershire batter clips it away through mid-wicket for an easy four.
Gareth Roderick follows his partner's lead by punching Henry Crocombe away square for another boundary in the next over.
Hampshire 61-1 v Warwickshire
Two fours in three balls off Oliver Hannon-Dalby have taken Hampshire past 50.
21-year-old Fletcha Middleton has moved onto 35. Remember (how to spell) the name. Middleton has got some future in this game.
Nick Gubbins joins the boundary party off Ed Barnard to bring up the 50 partnership too. They have added 25 off the last four overs.