Little is known regarding the reproductive biology of the white-faced saki. Although sakis have been in zoos since the mid-1970s, little attention has been paid to the reproductive biology of this threatened species. This study describes the results of a 3-year study of the reproduction of the white-faced saki in captivity. Using noninvasive methods to determine levels of estrone conjugates (E1C) and pregnanediol-3-glucuronide (PdG) in daily urine samples, we have characterized the female reproductive cycle of this species. Nonconceptive ovarian cycles were 16.95 ± 1.57 (SD) days, gestational length was 146.1 ± 5.2 (SD) days, and the length of lactationally induced infertility varied among females but averaged 163 ± 40.6 (SD) days. Attempts to accelerate puberty by pairing a young female with an adult male was without effect. Puberty occurred at 32 months of age in one female. This study provides information that enhances our understanding of the reproductive biology of this species. © 1995 Wiley-Liss, Inc.