Captive environments encompass various factors that can elevate stress levels and jeopardize the wellbeing of the captive animals. The use of positive reinforcement training (PRT) techniques enables researchers and caretakers to reduce tension directly associated with potentially stressful procedures and states. The current study tested the general effect of PRT on the wellbeing of zoo-housed chimpanzees (Pan troglodytes) by measuring behaviors that reflect poor and good welfare and that were not directly connected to the specific aim of the training session. The behavior of a group of twelve chimpanzees was measured throughout the day from the exhibition yard, at baseline (12 weeks) and during the PRT period (10 weeks). The results show a significant decrease in abnormal and stress-related behaviors and a significant rise in prosocial affiliative behaviors following implementation of the training program. The training was shown to have a greater positive effect on low-ranking individuals compared with high-ranking ones. This research shows for the first time that PRT offers an enrichment effect whose general influence lasts throughout the day, irrespective of any direct link to a specific trained behavior. Consequently, it can be claimed that PRT presents an effective enrichment tool that can be implemented with captive animals. Because of the above-noted differential effect between high- and low-ranking chimpanzees, however, this should be taken into consideration when combining PRT with the non-human primates' daily routine. Am. J. Primatol. 71:687–695, 2009. © 2009 Wiley-Liss, Inc.