Whereas verbal interactional behaviors have been repeatedly found to distinguish the families of persons with and without major psychiatric disorders, there has been comparatively little examination of the discriminative value of nonverbal interactional behaviors. We developed the Nonverbal Interactional Coding System to measure "affiliative" and "distancing" nonverbal behaviors in 18 schizophrenic and 18 bipolar patients and their parents during 10-minute interactions conducted during a posthospital period. Bipolar patients and their parents displayed affiliative nonverbal behaviors ("illustrator gestures" or "prosocial behaviors") for longer durations than schizophrenic patients and their parents. In contrast, parents of schizophrenic patients displayed distancing nonverbal behaviors (looking away) for longer durations than those of bipolar patients. The nonverbal interactional data added to the statistical strength of patients' and parents' verbal interactional data in distinguishing between these diagnostic groups. Nonverbal interactional behaviors are important variables to consider in interventions aimed at improving the communication skills of families coping with psychiatric disorders.