We report here on the social behavior of 30 adult male cynomolgus macaques (Macaca fascicularis), half of which were chronically administered propranolol HCl. All monkeys were maintained in groups of five, fed an atherogenic diet, and subjected to a social manipulation involving repeated disruption of social groups through redistribution of group memberships. One year of intensive behavioral observations were made, involving quantification of 27 kinds of social interaction typically exhibited by this species in captivity. Propranolol treatment resulted in a significant reduction in heart rate and blood pressure. Comparisons between propranolol-treated and untreated monkeys revealed no effects of beta-blockade on social dominance, aggressiveness, or active aspects of affiliation (e.g., grooming). The fact that few behavioral differences were found between conditions in this investigation indicates to us that such effects as were observed may owe as much to chance as to the action of the drug. Overall, these findings suggest that chronic beta-adrenergic blockade has minimal effects on the most prominent features of macaque monkey social behavior, especially those behavioral factors (aggressiveness and competitiveness) associated with risk for coronary disease in this species and in human beings.