The purpose of this study was to measure fathers' and mothers' linguistic involvements with the development of communication between young siblings. In a laboratory setting, 39 two-child mother-father families were videotaped in semistructured activities. The older sibling was from 18 to 26-months-old (M=22.4 months, SD=2.5 months) and the younger sibling was from 4 to 8-weeks-old (M=5 weeks, SD =1.5 weeks). Regardless of type of vocalization, when only one parent was present, utterances encouraging sibling interactions were more often aimed at girls than at boys. As a result, such utterances occurred more when both siblings were girls than for any other gender combination. Fathers were more active in issuing such utterances, especially to girls. When both parents were present, gender differences between parents disappeared, although the effects of children's gender did not. Overall, the results suggest that fathers very actively direct sibling interactions, especially those involving girls.