Data relating to infant feeding practices were obtained by a 6 week postnatal questionnaire from 459 women who participated in a randomised controlled trial of social support in pregnancy. They represented a 90% response rate from 507 women with a past history of a low birth weight baby before the index pregnancy. Thirty-nine per cent of the babies weighing more than 2500 g were breast fed completely. Women who experienced a delay of more than half an hour between birth and first suckling, and those who were given pethidine during labour breast fed for a shorter period, as did those who gave complementary bottle feeds. By considering the women's reasons for discontinuing or not initiating breast feeding, this paper suggests that improved social support from health professionals and others in the postnatal period can increase breast feeding success rates.