With Wednesday pace setter Carlos Checa leaving the Aragon test early in order to make his MotoGP return at Estoril this weekend, new World Superbike champion Max Biaggi took over at the top on Thursday.
Riding on a track layout slightly different to that used for the inaugural Aragon MotoGP round earlier this year, Aprilia rider Biaggi set a best lap time of 1min 58.7sec, which is 0.4sec behind the best by Checa on his Althea Ducati.
No less than four riders were credited with the second fastest lap time, with new Alstare Suzuki rider Michel Fabrizio, BMW's Troy Corser, PATA Aprilia's Noriyuki Haga and Kawasaki's Tom Sykes all lapping half a second behind Biaggi.
Sixth fastest was Biaggi's team-mate Leon Camier, making his return from injury at the test and only 0.1sec behind the second place riders, with fellow Briton Leon Haslam (BMW) seventh with a time of exactly two minutes.
Katsuaki Fujiwara (Kawasaki) was 0.2sec behind Haslam in eighth.
Testing concludes on Friday.