Rain showers interrupt preparation of the teams with McLaren-Mercedes finishing with a one-two in the session.
Jenson Button quickest in opening German Grand Prix practice
The 2009 world champion's lap time of 1 min 16.595 secs set early in the session at Hockenheim was enough for him to head the timings from McLaren-Mercedes teammate Lewis Hamilton, with Fernando Alonso, the world championship leader, third in his Ferrari.
Showers disrupted much of the session, leaving the teams to either sit in the garage and wait for conditions to improve, or head out on intermediate tyres.
Although conditions improved in the closing minutes enough for the drivers to return to slick tyres, Button's time remained unbeatable.
Pre-race favourite Sebastian Vettel was 11th in his Red Bull Racing car, with teammate Mark Webber down in 20th place.
Valtteri Bottas, the Williams third driver, crashed late in the session at Turn 13.
Second practice is at 4pm this afternoon.
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