World championship leader Maverick Vinales rebounded from his struggles in Barcelona with the fastest time across the first two practice sessions on Friday ahead of the Dutch MotoGP.
The Yamaha star finished a disappointing 10th at the Catalan GP a fortnight ago but comfortably outpaced German rookie Jonas Folger and defending champion Marc Marquez at Assen on a day that featured heavy rain.
Andrea Dovizioso, who has closed to within seven points of Vinales after back-to-back wins in Italy and Spain, was fourth quickest with veteran Italian Valentino Rossi sixth.
Spain's Vinales posted a best lap of 1min 33.130sec, with Folger 0.367sec behind, as most of the leading names made the top 10 with the exception of Ducati's Jorge Lorenzo, 14th at 1.393sec.
The 22-year-old, twice a winner at Assen in the support classes, tops the standings with 111 points after seven races, but four riders are within striking distance of the leader.