Estrone conjugates (EC), pregnanediol glucuronide (PdG), and estriol (E3) in urine, and immunoreactive EC, E3, pregnanediol (Pd), and progesterone (P,) in feces were determined along with records of perineal sex skin swelling throughout 7 nonconception cycles and 3 full-term pregnancies of 4 adult female bonobos (Pan paniscus). A typical preovulatory urinary E1C surge and postovulatory increase in urinary PdG were seen during the menstrual cycles. Fecal progestin levels were significantly correlated with those of PdG in urine in all cycles, while E1C measurements in feces were significantly correlated with those in urine in only 3 cycles. On the basis of hormone profiles, a variable follicular phase of 17-40 days and a relatively constant luteal phase of 11-15 days was found, resulting in cycle lengths of 31-51 days. All urinary and fecal hormones were markedly elevated during pregnancy. Measurement of EC in both urine and feces was most useful for early pregnancy diagnosis, while E3 was of value in confirming pregnancy and assessing fetal viability. The period of perineal swelling during the cycle comprised on average 66.3% of cycle length, half of which was associated with a phase of maximum tumescence. Ovulation usually occurred within the maximum swelling phase, but timing of ovulation within this period was highly variable and was more closely associated with the end rather than the onset of maximum tumescence. The data presented here are of great practical value in the captive breeding management of bonobos and offer new opportunities for investigating basic questions of bonobo reproductive biology both in captivity and in the wild.