The gonadal cycles of four groups of eastern oysters, Crassostrea virginica (Gmelin), including native stocks collected that year and inbred strains (reared in Delaware Bay for 5-6 generations) from both Long Island Sound and Delaware Bay, were compared in Delaware Bay in 1987. Inbred strains resembled their respective native stocks; both Long Island groups initiated gonadal development and spawning about one month earlier and spawned over a shorter duration than both Delaware Bay groups. Analysis of covariance revealed that the effect of time on gonadal development was statistically different (P ≤ 0.05) for all between-location group comparisons, but not for the two within-location comparisons. Thus, after six generations of inbreeding in Delaware Bay, Long Island oysters maintained their characteristic pattern of gonadal development and spawning, indicating the existence of genetically different environmental requirements for gonadal maturation between the two locations.