and H.M.Kubisch3,4

BACKGROUND: A decline in fertility is evident in human females past their middle thirties. This ‘reproductive senescence’, marked by a sharp decline in pregnancy rates, may be attributed to reductions in numbers of avail-able oocytes and their quality. Because Old World primates exhibit ovarian morphology and physiological control and timing of menstrual cycles closely resembling those of humans, the current study investigated the rhesus maca-que as a potential model for human reproductive senescence. METHODS: Ovaries collected from females aged 1–25 years and divided into five age groups were analysed histologically. RESULTS: General ovarian morphology demonstrated significant changes as the females approached menopause. The proportions of primordial and pri-mary follicles all demonstrated significant differences across age groups (primordial: 77.1, 79.9, 69.7, 62.9, 55.1%; primary: 21.5, 18.8, 28.5, 35.2, 43.1 % for age groups 1 to 5 respectively; P < 0.0001 for both). Samples from females approaching or undergoing the menopausal transition (aged 20–25 years) demonstrated evidence of ovar-ian senescence, having scattered and atretic follicles, low numbers of primordial follicles and reduced stromal tissue. CONCLUSION: This study supports the value of the rhesus monkey as a model for reproductive ageing because its ovary undergoes follicular reservoir depletion similiar to that seen in humans. Key words: follicle/oocytes/ovary/primates/reproductive agein