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.
Notts v Lancs 146-7
The key wicket!
Brett Hutton bowls Josh Bohannon with a delivery that nips back off the surface and clips the top of off stump. One that his team-mate Stuart Broad would have been proud of.
Hutton now has 4-53 and Lancashire have collapsed from 80-1 and 109-2 to be 146-7.
Worcs 136-6 v Sussex
An excellent delivery from Sean Hunt and it flies to the keeper from the shoulder of Gareth Roderick's bat.
He put on 92 in 22 overs with Adam Hose, who is still there on 52 and has been joined by Matthew Waite.
Yorkshire v Glamorgan 90-3
Possibly a chance goes begging for Yorkshire.
Marnus Labuschagne edges Mickey Edwards just wide of Finlay Bean at third slip. Bean tried to get down to it but to no avail.
Derbys v Leics 87-8
Image source, Rex FeaturesThe start of a new Henry Brookes over, and there is his first five-for in a Championship match.
It's not his best delivery, but Rehan Ahmed is caught behind down the leg-side as he tries to flick it away.
Brookes' only five-wicket haul for parent club Warwickshire came in the T20 Blast - although they are, of course, called Birmingham Bears in that competition.
Notts v Lancs 144-6
Tom Hartley is the new batter and early in his innings edges just past the slips for four, then sends a super drive square of the wicket for another boundary.
Another visiting player taking an attacking approach.
It's certainly advantage Nottinghamshire at the moment, though. Lancashire's chances of success in this match might hinge on how many more Josh Bohannon can score - he's 67 not out.
Image source, Getty ImagesDerbys v Leics 87-7
The morning session was all about Henry Brookes and Luis Reece as far as Derbyshire were concerned.
But it's Sam Conners who achieves their first breakthrough of the afternoon, with Tom Scriven caught behind for 12.
Chris Wight has come out to join Rehan Ahmed, who is 23 not out.
Somerset v Northamptonshire 117-2
It is very dark in Somerset. The lights have been burning bright for a while. It's also spitting.
The umpires are taking a reading as the players head back off. Not good.
They look like they might be hanging around on the other side of the rope rather than going inside. Maybe they think they'll be back on once this dark cloud slides over Taunton.
Essex 104-3 v Surrey
A jaffer.
Sean Abbott produces a perfect leg-cutter and that is a far more comfortable catch for Ben Foakes than the one he took to dismiss Alastair Cook before lunch.
Having reached 95-1, Essex are now under a bit of pressure and Surrey have their first bowling point.
Worcs 123-5 v Sussex
Image source, GettyAdam Hose drives for two and reaches his first Championship fifty for Worcestershire from 67 balls.
Given the circumstances, it's a hugely valuable knock for his side, who will want him to convert this good start into a big one.
Hose is 50 not out and Gareth Roderick has 28.
Worcs 121-5 v Sussex
Ollie Robinson has a five-for in his sights but he won't achieve it like that.
Gareth Roderick flashes away a cover drive for four - he didn't look totally in control of that - and then extravagantly flicks the next ball through the leg-side for four.
Somerset v Northamptonshire 116-2
Tom Kohler-Cadmore will feel much better. Craig Overton might even talk to him now.
Overton goes round the wicket and Sam Whiteman gets everything wrong as he nicks one to first slip where TKC makes absolutely sure this time.
If he'd done that nearly three hours ago then you feel Somerset would have been in a far stronger position.
Notts v Lancs 131-6
Two wickets now for Stuart Broad, but this one owes more to the catch by Haseeb Hameed at deep point.
Colin de Grandhomme was intent to attack from the outset and he drives uppishly on the offside - but Hameed makes an excellent grab diving forward just inside the boundary.
Image source, Getty Images
Hampshire 101-4 v Warwickshire
James Vince v Chris Woakes. This is what the County Championship is all about.
Hampshire have limped into three figures afer that bright start but if their skipper finds form then we know how destructive he can be.
Yorkshire v Glamorgan 83-3
A brief delay to play as one of the advertising hoardings has blown onto the outfield. A couple of Yorkshire fielders assist the Headingley staff in removing it. No harm done.
Essex 100-2 v Surrey
They are back out in the middle at Chelmsford and Jordan Clark begins the afternoon with a maiden over to Essex captain Tom Westley, who remains 16 not out.
Hampshire 93-4 v Warwickshire
Full and straight from Oliver Hannon-Dalby and Tom Prest doesn't get forward enough and is out plumb.
Ben Brown joins James Vince. The hosts need their older heads to step up here as the bowling has been a real challenge,
Hampshire are 10-3 in the last 21 balls.
Yorkshire v Glamorgan 83-3
No half-century for Sam Northeast, who is unable to add to his score after lunch.
Looks like he was trying to leave a Mickey Edwards delivery alone, but it strikes either the glove or the shoulder of the bat and pops into the grateful hands of Finlay Bean at slip.
Notts v Lancs 125-5
Magnificent start to the afternoon session by Lancashire and new batter Colin de Grandhomme, who sends his first ball to the fence for four with a lovely cover drive.
The next ball from Brett Hutton goes in roughly the same area and the New Zealand all-rounder runs three.
Hampshire 88-3 v Warwickshire
Ahhhh. So close to a fourth first-class half-century in just his seventh first-class innings.
The youngster has been outfoxed by wily Chris Woakes who produces a beauty to find the outside edge and feather a catch to the keeper. Took a peach to oust him.
Get on the Middleton bandwagon now while there is room left, there might not be for long... this 21-year-old opener can really play - several of his nine fours should come with a calorie warning, so delicious were they.
20-year-old Tom Prest is the next youngster tasked with facing in-form Woakes.
Stumped
Image source, PA MediaAmong the contributors on the latest episode of Stumped from BBC World Service is Steve Smith, who is making his debut for Sussex today, ahead of featuring for Australia in this summer's Ashes.
Also up for discussion is the volume of short-format cricket, plus an interview with Meg Lay, the first female member of groundstaff to work at an international venue in England.