In a sample of 55 black infants (age 5-6 months) living in the inner city in lower socioeconomic circumstances, 27 infants were being reared by their mothers in single-parent families. Male infants who had experienced minimal interaction with their fathers were significantly lower on the Bayley Mental Developmental Index and in measures of social responsiveness, secondary circular reactions, and preferences for novel stimuli. Female infants in this sample appeared unaffected by the father's presence or absence. After weighing alternative interpretations of the findings, we conclude that the father is a significant component in the early environment and that both observational studies and conceptual development of the role of the father in infancy are needed.