Ferrari struck an early blow on Monday with their 2008 car lapping quicker than the new McLaren in Formula One's first official test of the year in southern Spain.
World champion Kimi Raikkonen set the pace in Jerez with a lap time of one minute 19.845 seconds, according to the unofficial circuit timing.
Brazilian Felipe Massa was second fastest in the other Ferrari, with McLaren test driver Pedro de la Rosa third on the timesheets in 1:20.548 after sitting out the morning session due to the steady rain.
Ferrari-powered Toro Rosso, who will not be introducing their 2008 car until after the opening long haul races of the season, were fourth with German Sebastian Vettel at the wheel.
Brazilian Nelson Piquet junior made his first appearance for Renault since he was confirmed as a full race driver, with Spain's double world champion Fernando Alonso due to test on Tuesday in last year's car.
Briton Lewis Hamilton, the championship runner-up who partnered Alonso at McLaren last year, will also be in action on Tuesday.