Within the framework of the social stress and behavioral theories of depression, this study investigated the hypothesis that postpartum depression is a function of disruption of parents' prepartum functioning by the subsequent demands of infant caretaking. Seventy-eight primiparous married couples (N=156, 78 men and 78 women) volunteered to complete questionnaires at 8 weeks prepartum and 8 weeks postpartum assessing indicators of stress due to child care. The results indicated that when the level of prepartum depression was controlled, the amount of positive reinforcement reported experienced was significantly related to postpartum depression for women. For men, the degree to which their infant's behavior was viewed as better than the average baby was significantly related to postpartum depression. It was concluded that the findings supported a behavioral theory interpretation of postpartum depression. Implications for future research are discussed. (Author/MP)