The objective of this study was to improve human-animal management relationships by testing the effects of positive reinforcement training (PRT) on reducing human-directed aggression in rhesus monkeys (Macaca mulatta). Contra-aggression uses a combination of positive reinforcement training techniques designed to actively reduce instances of aggressive behavior. Additionally, this study looked at how much post-training generalization occurs between the staff who trains an animal and non-training staff interacting with trained animals. Three training treatments were applied: a non-training group (controls; N= 5), monkeys conditioned by a single trainer (ST; N- 5), and monkeys conditioned by multiple trainers (MT; N=5). Each macaque received two tests (human-intruder,husbandry-response) to evaluate behavioral changes prior to training, when training ceased, and after a 6-week non-training period. The tests assessed the level of training generalization to human interaction. There was no marked improvement in animal progression through the training plan from single to multiple trainers (P=0.927). which is inconsistent with current training philosophy; however, both single and multiple trainer groups showed a significant reduction of aggression (ST: P_< 0.001. MT: P< 0.001 ) during training. The two tests showed a marked reduction of aggression outside training sessions in the training groups (human intruder: P < 0.001; husbandry response: P = 0.01 ); however significance was not achieved in the non-training group. These preliminary results indicate that contra-aggression training and PRT in general can reduce aggressiveness in nonhuman primates, and such reduction could enhance their well-being during routine research and medical procedures.