The relative occurrence of outcrossing in two geographical populations of the digenetic trematode Lecithochirium rufoviride was investigated using starch gel electrophoresis to study the polymorphic locus Pgm-1. Assuming that the effects of mutation, genetic drift and natural selection on this locus are negligible, allozyme variation suggests the occurrence of extensive outcrossing in both populations, Ria de Arousa and Llanes (North of Spain). Therefore, the minimum outcrossing rate giving no statistically significant deviation respect to Hardy-Weinberg equilibrium was 70% and 66%, respectively. Despite of the asexual reproduction in the snail host, the possibility of self-fertilization as a component of the breeding system of this hermaphroditic helminth, and a population reproductive structure probably influenced by the habitat fragmentation, these results suggest that populations of this species in the definitive host, the European conger eel (Conger conger), are basically panmictic.