Over a 6-year period, a colony of Saimiri was established for experimental behavioral research. Heterosexual pair housing prevailed, and a number of offspring was produced. Females apparently underwent a lengthy adjustment process, inasmuch as viable infant production was infrequent until the female had been paired for three breeding seasons. Males required only a short period of adjustment, if any, to become effective breeders. Breeding was seasonal and births occurred during the summer. The mean maximum gestation for five females who delivered in one year was 162.6 days (range 152–168 days, n = 5). The short gestations for some of these females relative to those previously reported by other investigators suggest a broad range of variability in gestation for this species. The possibility that some of these five females conceived very soon after being paired with males is discussed with regard to social and coital influences on ovulatio