Jaime Alguersuari was the third fastest driver in Barcelona on Day 1 of the third pre-season test session.
The Toro Rosso driver, who was testing at his home track, completed 57 laps of the Circuit de Catalunya. His best effort of 1:25.638 was beaten only by world champion Sebastian Vettel and double world champion Fernando Alonso.
The team took advantage of some overnight rain to complete a 20 lap run on the intermediate Pirelli tyre before moving on to their scheduled dry-weather programme once the track had dried.
Alguersuari will be on testing duties in the STR6 again on Saturday.