Oral contraceptives were given on postpartum Day 5 to 363 patients; 83 were mothers breast feeding their infants. An additional 245 patients, including 91 who were breast feeding and did not wish to take the pills, served as controls. No significant difference was observed between the two groups of breast-feeding mothers who were able successfully to feed their infants for 6 weeks or more. The majority of patients taking pills had their first menstrual period prior to the 6 weeks evaluation. Side effects were minimal. Although subinvolution of the uterus was less in patients given pills, postpartum weight retention was higher. Patient acceptance was excellent, and no major problems were encountered.