Integrins were localized immunohistochemically in marmoset ovaries (Callithrix jacchus) of defined cycle stages. With monoclonal antibodies against beta 1, alpha 2, alpha 3, and alpha 6 integrin subunits, immunoreactivity was predominantly found in ovaries of the follicular phase. In the luteal phase, non-luteal cells, e.g. fibroblasts or endothelial cells expressed beta 1, alpha 2, or alpha 6 integrins. Immunostaining for the beta 1 subunit was strongest in granulosa cells of all growing follicles. Weak immunoreactivity was found in granulosa cells of atretic follicles, theca and interstitial cells. With the alpha 2 antibody, binding was evident in granulosa cells of many, but not of all, primordial and primary follicles. Expression of alpha 2 was also found in luteinized granulosa cells of tertiary follicles. In growing follicles, immunoreactivity of alpha 3 was restricted to granulosa cells of early secondary follicles. Within the epithelium, staining was almost exclusively found in granulosa cells bordering on the basal granulosa cell layer. In advanced stages of atresia, granulosa cells of antral follicles expressed the alpha 3 subunit. Integrin alpha 6 expression was evident in granulosa cells of all growing follicles but was absent during advanced stages of degeneration. The specific expression patterns of integrins suggest that these matrix receptors play a regulatory role during cyclic events in primate ovaries.