Jenson Button was fastest and his team mate Lewis Hamilton second as McLaren dominated a rain-hit opening practice for the German Grand Prix on Friday.
Intermittent showers made conditions tricky for the drivers although the rain was nothing on the scale that caused chaos at the British Grand Prix at Silverstone two weeks ago.
Valtteri Bottas crashed his Williams near the end of the session, smashing into the barriers on Turn 13 and emerging unscathed to survey the damage.
Button set the best time of one minute 16.595 seconds early in the session before the rain began while Hamilton, who will be taking part in his 100th Grand Prix on Sunday, was 0.498sec behind.
They were followed by world championship leader Fernando Alonso of Ferrari and Mercedes' Michael Schumacher. However, the conditions meant it was difficult to read anything significant into the timings.
The German Grand Prix is seen as crucial to McLaren's season after poor performances in the previous two races saw them slip down the standings.
The session was the debut for the new version of the cars following a series of upgrades.
The Red Bull pair made little impact with Sebastian Vettel 12th fastest and Mark Webber 20th. - Reuters
1 Jenson Button (Britain) McLaren - 1min16.595
2 Lewis Hamilton (Britain) McLaren - 1:17.093
3 Fernando Alonso (Spain) Ferrari - 1:17.370
4 Michael Schumacher (Germany) Mercedes - 1:17.382
5 Sergio Perez (Mexico) Sauber - 1:17.413
6 Nico Huelkenberg (Germany) Force India - 1:17.599
7 Nico Rosberg (Germany) Mercedes - 1:17.915
8 Felipe Massa (Brazil) Ferrari - 1:17.995
9 Pastor Maldonado (Venezuela) Williams - 1:18.020
10 Romain Grosjean (France) Lotus - 1:18.130
11 Kamui Kobayashi (Japan) Sauber - 1:18.226
12 Sebastian Vettel (Germany) Red Bull - 1:18.339
13 Valtteri Bottas (Finland) Williams - 1:18.422
14 Daniel Ricciardo (Australia) Toro Rosso - 1:18.709
15 Kimi Raikkonen (Finland) Lotus - 1:18.831
16 Jules Bianchi (France) Force India - 1:18.972
17 Jean-Eric Vergne (France) Toro Rosso - 1:19.039
18 Vitaly Petrov (Russia) Caterham - 1:19.674
19 Heikki Kovalainen (Finland) Caterham - 1:19.963
20 Mark Webber (Australia) RedBull - Renault 1:20.122
21 Charles Pic (France) Marussia - 1:20.169
22 Timo Glock (Germany) Marussia - 1:20.539
23 Pedro de la Rosa (Spain) Hispania - 1:21.138
24 Dani Clos (Spain) Hispania - 1:21.740