Methoxychlor (MXC), an organochlorine pesticide, inhibits growth and induces atresia of antral follicles in rodents. MXC metabolites, mono-OH MXC (mono-OH) and bis-OH MXC (HPTE), are thought to be more toxic than the parent compound. Although studies have examined effects of MXC in rodents, few studies have evaluated the effects of MXC in primates. Therefore, the present study tested the hypothesis that MXC, mono-OH, and HPTE inhibit growth and induce atresia of baboon antral follicles. To test this hypothesis, antral follicles were isolated from adult baboon ovaries and cultured with vehicle (dimethylsulfoxide; DMSO), MXC (1-100 micro g/ml), mono-OH (0.1-10 micro g/ml), or HPTE (0.1-10 micro g/ml) for 96 hr. Growth was monitored at 24 hr intervals. After culture, follicles were processed for histological evaluation of atresia. MXC, mono-OH, and HPTE significantly inhibited follicular growth and increased atresia compared to DMSO. Moreover, the adverse effects of MXC and its metabolites on growth and atresia in baboon antral follicles were observed at lower (100-fold) doses than those causing similar effects in rodents. These data suggest that MXC and its metabolites inhibit growth and induce atresia of baboon antral follicles, and that primate follicles are more sensitive to MXC than rodent follicles.