Italy's Marco Simoncelli topped the timesheets in both practice sessions for the German MotoGP at Sachsenring.
The Honda rider pipped championship leader Casey Stoner by 0.181 seconds in the first and reigning champion Jorge Lorenzo by 0.095 in the second.
Ducati's Valentino Rossi endured a miserable Friday, with a lowly 14th and 12th to show for his efforts.
Britain's Cal Crutchlow could only muster the morning's 13th best time, and slipped to 14th in the afternoon.
The morning session was run in cold, windy conditions and Rossi, Stoner, Crutchlow, Dani Pedrosa and Toni Elias all came off at various points but escaped serious injury.
Rossi's bike was also hit by electrical problems toward the end of the second session, while Hector Barbera crashed out at the end of it but was left unhurt.
France's Sylvain Guintoli stepped in to replace Loris Capirossi for the afternoon and the rest of the weekend.
Pramac Racing rider Capirossi is still suffering from the effects of a crash at Assen which forced him to miss the Italian MotoGP.
Stoner heads the standings with 152 points going into Sunday's race, with Lorenzo on 133 and Italian Andrea Dovizioso on 119.
German MotoGP first free practice:
1. Marco Simoncelli (Ita/Honda) 1min 22.924sec
2. Casey Stoner (Aus/Honda) at 0.181sec
3. Jorge Lorenzo (Spa/Yamaha) 0.223
4. Nicky Hayden (US/Ducati) 0.382
5. Andrea Dovizioso (Ita/Honda) 0.532
6. Karel Abraham (Cze/Ducati) 0.593
7. Hector Barbera (Spa/Ducati) 0.610
8. Randy de Puniet (Fra/Ducati) 0.711
9. Ben Spies (US/Yamaha) 0.735
10. Colin Edwards (US/Yamaha) 0.771
11. Dani Pedrosa (Spa/Honda) 0.781
12. Alvaro Bautista (Spa/Suzuki) 1.166
13. Cal Crutchlow (GB/Yamaha) 1.339
14. Valentino Rossi (Ita/Ducati) 1.689
15. Hiroshi Aoyama (Jpn/Honda) 1.797
16. Toni Elias (Spa/Honda) 3.237
17. Loris Capirossi (Ita/Ducati) 3.511
Second free practice:
1. Simoncelli 1min 22.225sec
2. Lorenzo at 0.095
3. Pedrosa 0.207
4. Stoner 0.317
5. Dovizioso 0.429,
6. Hayden 0.657
7. Spies 0.669
8. De Puniet 0.812
9. Bautista 1.036
10. Abraham 1.127
11. Edwards 1.206
12. Valentino Rossi 1.308
13. Barbera 1.400
14. Crutchlow 1.535
15. Aoyama 1.681
16. Elias 2.079
17. Guintoli 3.739