Interactions between unrelated and related silverback-infant dyads are compared in an attempt to assess the influence that kinship may have on male parental behavior. Observational data were collected on each member of two silverback-infant dyads, in two separate enclosures at the Lincoln Park Zoo in Chicago, IL. The silverback was the father of the infant in one dyad, and unrelated to the infant in the other. Each infant was responsible for initiating most of the encounters with its respective group silverback. However, based on the frequency and duration of interactions, there is a significantly higher degree of affiliation and tolerance within the silverback-offspring dyad. Furthermore, the unrelated infant was the recipient of more than 40% of the agonistic behaviors exhibited by the silverback, whereas no such encounters were recorded within the related dyad. Although alternative explanations must be considered, these findings are consistent with kin selection theory, are similar to observations documented for wild mountain gorillas, and provide uncommon comparative data on adult male interactions with related and unrelated infants. In addition, this study offers behavioral information relevant to the management of captive gorillas, which often requires the introduction of immatures into non-natal groups. Zoo Biol 18:53–62, 1999. © 1999 Wiley-Liss, Inc.