A balanced social group of 17 rhesus monkeys, wild-trapped in northern India, was established in a colony cage of 1000 square feet in Calcutta. Quantitative data were obtained on behavioral repertoire, activity patterns and social interactions. Experiments were conducted to study the effect of certain environmental and social variables on the expression and intensity of intragroup agonistic behavior. A 25% food reduction resulted in no change in agonistic interactions, whereas a 50% food reduction and starvation regime resulted in a significant decrease in agonistic behavior. Investigative behavior increased, but grooming, sexual behavior, play, and aggressive behavior decreased. The monkeys became lethargic. The behavior of the monkeys resembled human behavior in famine and experimental starvation. A significant increase in agonistic behavior occurred when the distribution of the food was restricted, but the amount of food remained normal. Highly significant increases in the frequency and intensity of agonistic behavior occurred with the introduction of new monkeys who were social strangers. These results agree well with those of BERNSTEIN et al. on rhesus and KAWAI on Japanese macaques. The age and/or sex class corresponding to that of the introduced monkeys was the one which initiated most of the threat and attack behavior. A significant increase in agonistic behavior also occurred with a space reduction from 1000 square feet to 500 square feet. In general, social changes (i.e., changes in group membership) had a far greater impact on levels of intragroup aggression than did environmental changes such as starvation and crowding.