DNA fragmentation (apoptosis) was studied during the follicular, periovulatory and luteal phase in the marmoset monkey ovary by means of terminal transferase mediated in situ nick end labeling, and correlated with immunohistochemical localization of integrins (beta 1, alpha 2 and alpha 6 subunits). For this purpose a double-labeling technique was developed. During all phases, apoptosis of granulosa cells was exclusively restricted to tertiary follicles displaying advanced stages of atresia (as morphologically determined). During early stages of atresia in tertiary follicles, indicated by widened intercellular spaces, no apoptosis was seen. Staining intensities for integrins beta 1 and alpha 6 were strong in intact primordial/primary, secondary and tertiary follicles. Integrin expression of granulosa cells was weak in atretic tertiary follicles but not in atretic primary or secondary follicles. Double labeling revealed that DNA fragmentation was solely found in granulosa cells of tertiary follicles displaying faint or absent staining for both integrin subunits. During the periovulatory and the luteal phase, granulosa cells of atretic tertiary follicles bordering on the basal membrane, which were referred to as luteinizing cells, expressed the beta 1 subunit as well as the alpha 2-integrin subunit whereas granulosa cells neighboring to the antrum were apoptotic and negative for integrin immunoreactivity. In summary, early atresia of tertiary follicles is first characterized by morphological alterations as wide intercellular gaps, without any signs of granulosa cell apoptosis. Advanced stages of atresia, in tertiary follicles however, are accompanied by apoptosis of granulosa cells and a faint or absent staining for integrin subunits beta 1 and alpha 6. According to recent in vitro findings, our results point to a possible relation between granulosa cell apoptosis of tertiary follicles and integrin expression in ovarian marmoset follicles.