Abstract
The replacement of a sexually mature, but sexually inactive, male by a novel mature male in a small colony of Macaca fascicularis brought about changes in social behaviour and structure. Particularly striking were the heightened levels of all sexual activity, especially in the females' invitation to the male to copulate. Cohesiveness around the male increased. Increased levels of agonism were noted and changes in the agonistic female hierarchy resulted. The grooming relationships in the colony were also significantly altered.