Valentino Rossi arrives in California back on top of the MotoGP World Championship and seeking a repeat of last year's classic victory in Sunday's United States Grand Prix.

With two successive victories including his 100th grand prix win at Assen last Saturday, the 30 year old Fiat Yamaha rider has prised open a slim five point lead over team-mate Jorge Lorenzo with Casey Stoner a further four points adrift in third place.

Nobody who witnessed Rossi's win last year's Laguna Seca race will forget his performance. The Italian rode like a man possessed to beat Stoner, who had dominated practice and qualifying on the factory Ducati, and Rossi's overtaking move as they plunged through the famous Corkscrew turn is already embedded in MotoGP folklore.

While Rossi arrives this week brimming with confidence Stoner faces worrying problems regarding his health. For the last two grands prix the tough Australian has suffered from severe stomach cramps during the race.

Both times, after finishing third behind Rossi and Lorenzo, he has been helped off his machine and gone to the medical centre. The former world champion is desperate to discover the cause of the problem but only has an eight day gap between the races in Holland and America.

Lorenzo's one and only appearance at Laguna last year resulted in another spectacular accident that was the hallmark of the first part of his MotoGP debut season. But he returns in a very different frame of mind. The 21 year old Spaniard has won two grands prix this season and has only crashed in one race. The former double 250cc world champion is five points behind Rossi in the championship but will need some better starts if he's going to beat his team-mate at round eight.

The Repsol Honda duo of Dani Pedrosa and Andrea Dovizioso couldn't wait to get on the plane after a disastrous Dutch TT. Both crashed out in separate incidents at turn one while holding fourth. Last year Italian Dovizioso made an impressive Laguna debut in fourth place while Pedrosa missed the race with a hand injury sustained in a crash while leading the previous German Grand Prix.

The American duo of Colin Edwards and Nicky Hayden return home after contrasting fortunes this year. Former World Superbike champion Edwards is flying on the Monster Tech 3 Yamaha which was endorsed by his excellent fourth place in Assen and four years ago he finished second at Laguna. The race in 2005 was won by Hayden and he repeated the feat a year later on course to the world title.

This year Hayden has become the latest big name to struggle on the Ducati but at Assen there were glimpses that he was getting to grips with the GP9 Desmosedici machine. He eventually finished eighth in a hectic fight to the line, despite a loose handlebar, and there would be no better place than home for the confidence to continue.