Serna's feature work began with a bit part in "The Student Nurses" (1970). He received more attention playing a rooster owner in the cock-fighting scene of "Day of the Locust" (1975), was an arms dealer in "Deal of the Century" (1983) and a patriotic father of the Latino member of the freedom fighters in "Red Dawn" (1984). In "Silverado" (1985), Serna was a hired gun while in "American Me" (1992) he was alongside his former "Zoot Suit" co-star Edward James Olmos playing a hardened criminal. Paul Rodriguez gave Serna a supporting part in "A Million to Juan" (1994) and in Johnny Depp's directorial debut "The Brave" (lensed 1996), he was cast alongside Marlon Brando.
Serna first began appearing in TV-movies in 1974 with "The Gun" (ABC). He had one of his best roles as the younger brother of the slain president in "Sadat" (syndicated, 1983). Although Serna made numerous unsold TV pilots, including one for "Car Wash" (NBC, 1979), his first regular series role was as a co-ed's overprotective father in the short-lived CBS effort "Second Chances" (1993-94). He reprised the same character, now the over-protective father of a hard-working Latina, in "Hotel Malibu" (CBS, 1994), a summer series.