Thirty-five live births were recorded over a 5-year period from three subspecies of the mitis (Sykes and blue) monkey (Cercopithecus mitis) maintained outdoors in single-male harem breeding groups. There was no indication of birth seasonality. Females of one subspecies, C. m. kolbi, were individually caged, and basic reproductive parameters were monitored. A menstrual cycle length of 31.9 ± 6.0 days was recorded, and there were a large number of irregular cycles. Within individuals, mean progesterone and estrogen concentrations during the luteal phase of the cycle ranged from 5.5 to 10.7 nmol/liter and from 542 to 829 pmol/liter, respectively. Attempts at timed matings were unsuccessful. It is concluded that the mitis monkey is slow to adapt reproductively to captivity and is, therefore, not especially well-suited for routine reproductive studies. However, it may prove valuable to elucidate some of the more complex factors controlling guenon reproduction.