Reproductive activity is seasonal in bandicoots. To determine the seasonal changes in the reproductive tract of the male bandicoot, the morphology of the testis and the prostate was examined during the breeding and non-breeding season. Although the dimensions of the testes of the bandicoot did not change with season, the volume of testicular Leydig cell tissue increased about twofold and this change within the testis was accompanied by a threefold increase in prostate gland size. The bandicoot prostate can be divided into two zones, a dorsal zone which produces a carbohydrate secretion containing the enzyme acid phosphatase, and a smaller ventral zone which produces a mucoprotein secretion lacking acid phosphatase activity. These morphological changes within the testis and the prostate gland of the male bandicoot correlate with the seasonal variation in plasma testosterone concentrations previously reported. The testosterone concentration in the male starts to rise in May and reaches a peak in September and presumably causes the increase in prostate gland size and activity.