The extent of isomorphism between parent-child to child-friend microsocial interactions was studied by means of videotaped laboratory and observation coding procedures. Similar tasks, coding systems, and behavior clusters were used to describe the topography of parent-child and child-friend interactions. A total of 200 boys were observed while they interacted with their parents at 10 and 14 years of age, and with a close friend when they were 14. Longitudinal comparisons of the rate per minute of behavior clusters indicated an increase in social aggression from ages 10 to 14 in parent-child interactions. Isomorphism between parent-boy and friend-boy interactions was limited: restricted to low, but statistically reliable, positive correlations between the use of the variables"directives" and "laugh" across the interpersonal spheres. The exchange of directives in parent-child interactions was negatively correlated with the variable "converse" in the friend-boy interaction. Multivariate analyses revealed that the combined tendency correlated with the canonical dimension relating family to friend microsocial processes. It was concluded that the form of the interpersonal behavior in adolescent friendships was process-driven and heavily influenced by the social niche, selected by the boys, within which intimacy was established. (Author/RH)