F1 and F2 progeny of two diallel crosses among Centrosema virginianum accessions were grown at several sites in Queensland, Australia, and herbage yield was measured. Both diallel crosses showed significant genetic variation, but there were marked differences in the type of genetic variation present. In the first diallel cross, which was based on six unselected parents, genetic variance was predominantly additive and was associated with large differences in leaf size. In the second diallel cross among six parents selected for superior yield, genetic variance was predominantly non-additive and was associated, at least partly, with differences in seed production and/or phenology of the crosses. Genotype x site interactions appeared to be more important in the second diallel cross than in the first. Genotype x year interactions occurred in the second diallel cross.