Hamilton fastest in France
Teams start preparations for Monaco
Lewis Hamilton topped the timesheets at the end of the opening session of a three-day test at the Paul Ricard circuit in France.
The McLaren ace lapped the 3.593-km track layout in a best time of one minute 5.6 seconds.
Hamilton will hand over driving duties to his teammate Heikki Kovalainen on Friday, as the team attempt to prepare their car for the unique test of Monaco at the end of the month.
The sole Ferrari of championship leader Kimi Raikkonen was second quickest on Thursday, almost half a second slower than Hamilton having completed 19 more laps, while BMW-Sauber's Robert Kubica was third after 124 laps.
Red Bull Racing's Mark Webber finished the day in fourth place ahead of stable mate Sebastian Vettel, who impressed in the new Toro Rosso car with a time of 1min 6.372secs, less than three hundredths of a second behind Webber's sister car.
Nico Rosberg, who completed a mammoth 154 laps in the Williams FW30, was sixth.
Alex Wurz was seventh for Honda with a best time of 1:06.681, while Toyota tested a number of Monaco-specific aerodynamic revisions as Timo Glock went eighth fastest.
Tonio Liuzzi was ninth for Force India, while Renault's test driver Luca di Grassi was the slowest of the 10 drivers on show, posting a best lap almost two seconds slower than Hamilton's benchmark.