Ducati's Andrea Iannone was quickest during opening practice for the Dutch TT at Assen, closely followed by team-mate Andrea Dovizioso with the pair split by two-tenths at the top of the timing screens.
The Italian rider is set to start the race at the back of the grid following his collision with Jorge Lorenzo last time out in Barcelona, but that didn't put him off showing what Ducati can do as he topped the leaderboard for much of the session.
Tech3 Yamaha rider Pol Espargaro was third, a further tenth back, followed by Scott Redding and Danilo Petrucci on identical times – 1m34.660s – to give Ducati four of the top five positions.
Jorge Lorenzo was sixth, 0.373s off the pace, only just outpacing team-mate Valentino Rossi in seventh.
Honda seemingly struggled around Assen, failing to make the top ten as championship leader Marc Marquez finished 11th, more than six-tenths down on Iannone.
