A prenatal intervention designed to prevent the onset of major depressive episodes (MDEs) during pregnancy and postpartum was pilot tested at a public sector women's clinic. The "Mamas y Bebes"/Mothers and Babies Course is an intervention developed in Spanish and English that uses a cognitive-behavioral mood management framework, and incorporates social learning concepts, attachment theory, and socio-cultural issues. The four goals of this project were to develop the intervention, assess its acceptability, test the feasibility of conducting a randomized trial with public sector patients, and obtain estimates of its effect size. Forty-one pregnant women at high risk for developing MDEs were randomized to the Mothers and Babies Course (n = 21) or a comparison condition (n = 20). Assessments occurred during pregnancy and at 1, 3, 6, and 12 months postpartum. Differences in terms of depression symptom levels or incidence of MDEs between the two groups did not reach statistical significance in this pilot trial. However, the MDE incidence rates of 14% for the intervention condition versus 25% for the comparison condition represent a small effect size (h = 0.28) that will be further examined in a larger scale study. The intervention was well received by the participants and implementation of a randomized trial appeared quite feasible as indicated by our follow-up rate of 91% at 12 months. Implications for the continuing development of preventive interventions for perinatal depression are discussed. (Contains 1 figure and 3 tables.)