An earlier study of mothers of premature and full-term infants showed that the type and amount of social interaction between a human mother and her infant in the immediate postpartum period can influence the mother's subsequent behaviour and attitude towards the infant. Separation of a mother from her infant for as short a time as three weeks in the immediate postpartum period can lead to lowered feelings of maternal competency and decreased amounts of attachment behaviour, sometimes continuing for as long as one month after the pair have been reunited. Follow-up of these mothers and infants at 11, 12 and 15 months after discharge from the hospital showed that the effects of separation on maternal attitude and behaviour had disappeared, except that non-separated mothers continued to touch their infants more than separated mothers. Differences in maternal behaviour varied with birth order and sex of the infant and social class membership of the family. These findings are discussed in terms of ethological and social learning theories as they apply to matenal 'social attachment' in the neonatal period. The importance of considering the consequences of neonatal separation for the entire family rather than mother alone is emphasized.