Summary. Data were obtained from post-mortem investigations of 190 culled and road-killed muntjac bucks between 1967 and 1989. Although adult bucks (i.e. those having undergone at least one antler cycle) have a synchronous annual antler cycle, unlike temperate-zone cervids there was little seasonal variation in testis size or activity, or in the size and activity of the epididymidis or accessory reproductive glands. Spermatogenesis was not abated when the antlers were in velvet and year-round fertility was achieved without additional sperm storage. There was little seasonal change in plasma testosterone concentrations in samples obtained from captive and free-living bucks although castration caused antler casting and prevented mineralization. Hence the data are equivocal as to the role of steroids in driving the antler cycle; experimental work on this species would be valuable in examining the mechanisms which regulate the antler cycle.