The effects of the familiarity of setting and partner on the social behavior of infants was studied. Subjects were 22 infants 6-18 months old. Eleven of the infants were in a day care center; the remainder were cared for at home. In the first portion of the study, the day care infants were observed interacting with each other in the nursery setting. Later, an unfamiliar infant (not in day care) was paired with a day care infant and observed for 15 minutes three times at weekly intervals. All incidents of social behavior was recorded by an observer. A greater incidence of social behavior was observed in the familiar-unfamiliar pair. An exploration of novelty explanation was given for this finding. (ST)