His consistent performances in midfield awarded him a lucrative transfer to S.S. Lazio in the Italian Serie A, in 2001.
There he became suddenly popular amongst Lazio's fans because of a late equalising goal scored in the very last minute of a derby against cross-city rivals AS Roma that were leading the game 2–1 until then.
During that tournament, Vélez' coach Miguel Ángel Russo, seeing the team's position of right and left winger were well covered by Jonás Gutiérrez and Marcelo Bravo, used Castromán as a second striker.
Castromán played at great level in his new position, and was the team's topscorer along Rolando Zárate during the aforementioned Clausura tournament.
[3] After personal differences with Vélez Sársfield coach, Ricardo La Volpe, Castromán decided it was time to change teams, joining Club América of Mexico.