This study investigates three types of reciprocal interactions among members of the family unit (father, mother and infant): father-infant interaction affecting child's development, father-infant interaction affecting mother's behavior, and husband-wife interaction affecting mother's behavior. Data from a sample of 39 healthy first-born infants (20 male and 19 female) and their white, middle-class parents were collected independently in several ways: (1) infants, 3 days old, were examined in the hospital nursery and evaluated on alterness, motor maturity, and irritability; (2) ratings were made of the quality of the mother-infant relationship in connection with two time-sampling home observations when the infants were 4 weeks old; and (3) fathers were interviewed by a male psychiatrist when the infants were 4-5 weeks old. The network of significant correlations found for male infants is illustrated with a diagram and discussed. No significant correlations were found for female infants. (Author/ED)