In this study, the influence of paternal involvement in caregiving on infant sociability was assessed using a strange situation paradigm adapted from the work of Ainsworth, Blehar, Waters, and Wall (1978). Thirty-seven families participated with their firstborn child (aged 12-14 months). According to the questionnaire, 20 nontraditional fathers were very involved in caretaking, and 17 fathers were less or not at all involved. Infant sociability was assessed using three of Ainsworth et al.'s rating scales: proximity or contact-seeking, avoidance, and distance interaction. Results indicated that infants of nontraditional fathers were globally more sociable with all their partners (father, mother, and stranger) than infants of traditional fathers. Furthermore, results suggested that it was not only the father-infant relationship or infant development which were affected by the amount of paternal involvement in daily caretaking but the family system as a whole. Indeed, infants from nontraditional families appeared to interact equally with their fathers and mothers in direct interaction. In addition, these infants interacted at a distance with a stranger as much in the presence of their fathers as in the presence of their mothers, thereby suggesting that both parents represented an equally secure base.