The ovarian cycles of four adult female spider monkeys (Ateles geoffro
yi) were followed daily throughout 30 days by means of vaginal swabs a
nd blood samplings. Cytological analyses of the vaginal swabs and radi
oimmunoassay determination of the daily levels of estradiol-17 beta (E
-2) and progesterone (P-4) wer done in order to classify the kind of o
varian cycle of this species. Our results show that Ateles geoffroyi f
emales display menstrual cycles of about 24 days on average. By compar
ison with the well-known menstrual cycles of women, apes, and Old Worl
d monkeys, the four distinctive cytological phases (bleeding, follicul
ar, periovulatory, and luteal) could be recognized; mid-cycle E-2 peak
s followed by mid-luteal increases of the same hormone were present in
all four females. P-4 levels were higher after the E-2 peak, although
both hormones were present throughout the cycles. Also, age-dependent
features, hormone profiles, and changes in menstrual phases lengths w
ere detected. (C) 1998 Wiley-Liss, Inc.