This weekend's German MotoGP began with five big accidents in the first 20 minutes of Sachsenring track action.
All but one occurred at the fearsome Turn 11, a fast right-hander at the crest of a hill, and the incidents are sure to raise pressure on Bridgestone over the warm-up characteristics of its tyres.
World Championship leader Stoner was first to go, suffering a brutal highside from his Repsol Honda through Turn 11 - one of the few right-hand corners - on his out lap.
All of the others were lowside falls, although it is possible that Stoner had lost the front moments before losing the rear and being pitched into the air.
Toni Elias and Valentino Rossi then fell at the same corner - with Rossi sliding along the asphalt at high speed, before being flicked into air as he hit the lip of the gravel trap.
The Ducati star immediately looked at his right elbow, where his leathers were visibly damaged, and went straight to the Clinica Mobile to have it checked, before getting back on track with five minutes to go.
After Rossi's spill, Elias had his second big fall, this time at turn one, leaving the LCR Honda rider without any bikes.
While Elias was walking away, countryman Dani Pedrosa - who made his comeback from a broken collarbone last time at Mugello - lost the front of his factory RCV through Turn 11 and bounced harshly through the gravel. The Spaniard escaped without further injury.
The second half of the session saw no more falls, and ended with Marco Simoncelli on top by 0.181sec from Stoner, with Mugello winner and reigning world champion Jorge Lorenzo 0.223sec from the top in third.
Rossi's team-mate Nicky Hayden (+0.382sec) was fourth at a track he has a strong record at, with Andrea Dovizioso the only Repsol rider to stay on two-wheels in fifth (+0.532sec).
Rookie Karel Abraham made a strong start to the session with sixth (+0.593sec) for Cardion AB Ducati, with Hector Barbera (Aspar), Randy de Puniet (Pramac), Ben Spies (Yamaha) and Coin Edwards (Tech 3) completing a top ten covered by 0.771sec.
Loris Capirossi, returning to action after missing two races with rib and shoulder injuries, was 17th and last. The Italian veteran is uncertain for the rest of the weekend.
Free practice (1)
8. de Puniet