Social subordination is associated with impaired reproductive success among female macaques living in natural or "semi-natural" environments. We studied the relationship between social status and ovarian function in female cynomolgus macaques living in socially stable single-male harem groups or in groups of like composition in which social instability was induced by the frequent redistribution of female group members. Compared to socially dominant females, socially subordinate females had fewer ovulatory menstrual cycles, more cycles with deficient luteal phase plasma progesterone concentrations, increased adrenal weights and increased heart weights. Social instability influenced none of these variables. In fact, females living in the situations of induced social instability had higher luteal phase plasma progesterone concentrations; this may be the result of frequent exposure to novel males. The results indicate that impaired reproductive success observed in socially subordinate female macaques may be related, at least in part, to changes in ovarian endocrine and ovulatory function.