Peter Hickman, a Superstock winner here last year, is top of the list in Tuesday's practice session.
West Yorkshire rider Jamie Coward is the top man in the Supertwin class. The 28-year-old's average speed was 108.42mph.
Dean Harrison tops the times in Superbike practice. The 30-year-old English rider's best finish at the North West was second place in this class last year.
The average speed of his Kawasaki was 121.21mph with local lad Michael Dunlop next on 120.97.
Northern Ireland's Alastair Seeley, winner on a record 24 occasions here, tops the first practice times in the Supersport class.
His average lap speed was 116.55mph, with Lee Johnston next on 116.47.