Postpartum factors affecting the duration of lactation were identified for 250 women through a telephone survey. The survey examined the behaviors and attitudes of women who had chosen to nurse and who were still nursing at 2 weeks postpartum. Sixty percent of the mothers nursed their infants after delivery. However, by 10 weeks postpartum, only 34% of the babies were still breast fed. By self-report, the most significant factors associated with the maintenance of lactation at 10 weeks were related to perinatal hospital protocol, especially letting the infant suckle soon after birth. Other significant predictors of successful lactation outcome included early milk "let down," little use of supplemental formula, the mother's expectation at parturition of an extended nursing period, her feeling well and being satisfied with her body weight, her previous successful experience with lactation, and her perception that she feeds her infant on demand. Few of the women who had stopped nursing after 2 weeks sought advice on breast feeding from anyone other than the pediatrician. Most coped with their nursing problems themselves. The data reinforce the importance of labor and delivery practices that support early maternal-infant contact. They also suggest the use of infant health indexes and weight and height percentile placement records rather than reliance solely on weight gain as the index of lactation adequacy. Further, they indicate the need for clinical intervention before 2 weeks postpartum.