Spermatozoa distend the uterus of the overwintering pipistrelle bat and their relationship with the uterine epithelium has been examined. The epithelium actively secretes PAS-positive material and spermatozoa are found orientated with their heads directed towards it over large areas. Electron microscopy has revealed that microvilli originating from the epithelial cells are commonly in contact with the cell membrane of the spermatozoa. It is suggested that this contact may constitute one of the pathways by which nutrient material from the endometrium is transferred to the stored spermatozoa and may account, in part, for the prolonged survival of the spermatozoa in this species. The relationship between spermatozoa and their storage organs is briefly reviewed.