Reigning MotoGP champion Jorge Lorenzo
began the Dutch TT weekend on top of the timesheets during a cold but dry Thursday morning practice at Assen.
The Factory Yamaha star led most of the 45-minute session - barring a brief interruption by Repsol Honda riders Marc Marquez and Dani Pedrosa
on the edge of the ten minute to go mark - to finish 0.350s clear of Tech 3 Yamaha's Cal Crutchlow.
Lorenzo's best lap was 0.7s from the race record.
Rookie Marquez proved to be the leading Honda rider in third (+0.620s), followed by Lorenzo's team-mate Valentino Rossi. The Italian, eager to try a new set-up that brought promising braking gains at the Aragon test, held second for parts of the session but ultimately lapped +0.695s from Lorenzo.
World championship leader Pedrosa, whose title lead has shrunk to seven points after victories for Lorenzo at the last two rounds, was the final rider within one second of Lorenzo.
Sixth position went to top CRT rider Aleix Espargaro (+1.167s) while Stefan Bradl, who has swapped from Nissin to Brembo brakes in an attempt to improve front end feel, began the weekend seventh quickest for LCR Honda.
Alvaro Bautista, who collided with Lorenzo at turn one of last year's Dutch TT, was seventh for Honda Gresini with Pramac Ducati stand-in Michele Pirro the top Ducati on the lab version of the GP13.
Crutchlow's rookie team-mate Bradley Smith, fresh from another round of hand surgery, completed the top ten.
Hiroshi Aoyama, injured at Catalunya, is being replaced at Avintia by team test rider Ivan Silva., who was 23rd quickest on his MotoGP return.
The first Dutch TT ('Tourist Trophy') was held in 1925 on a 28.4km road circuit around Assen, reduced to 16.5km by the time of the inaugural 1949 motorcycle grand prix season.
A new 7.7km circuit was then built in 1955, while the most recent re-design cut the length to 4.5km for 2006. Assen is the only venue that has remained on the calendar since the inaugural 1949 season and the Dutch TT is always held on the last Saturday in June.Free practice (1):
1. Jorge Lorenzo
2. Cal Crutchlow
3. Marc Marquez
4. Valentino Rossi
5. Dani Pedrosa
6. Aleix Espargaro
7. Stefan Bradl
8. Alvaro Bautista
9. Michele Pirro
10. Bradley Smith
11. Andrea Dovizioso
12. Nicky Hayden
13. Karel Abraham
14. Hector Barbera
15. Randy De Puniet
16. Andrea Iannone
17. Danilo Petrucci
18. Yonny Hernandez
19. Colin Edwards
20. Claudio Corti
21. Michael Laverty
22. Bryan Staring
23. Ivan Silva
24. Lukas Pesek