After placing both cars on the podium in Bahrain, Lotus again showed its speed as French driver Romain Grosjean led the morning testing session on Wednesday at the Mugello circuit.
Grosjean clocked a best lap time of 1 minute, 21.603 seconds, 0.294 ahead of Red Bull's Mark Webber, with Ferrari's Felipe Massa 0.654 behind in dry conditions.
Two weeks ago, Lotus teammates Kimi Raikkonen - who is not testing this week - and Grosjean placed second and third in the Bahrain Grand Prix.
Ferrari's Fernando Alonso was fastest under the rain Tuesday.
Two-time defending world champion Sebastian Vettel of Red Bull was scheduled to drive later Wednesday, as well as during the third and final day of testing Thursday.
The next race is the Spanish Grand Prix on May 13.