This study aimed to assess the conditions under which monkeys might produce common effects in an instrumental task. One group of Tonkean macaques (Macaca tonkeana) and two groups of rhesus macaques (M. mulatta) were given series of tests in which food incentives were placed under stones of various weights. In the Tonkean group, the simultaneous action of two subjects in moving the same stone was a relatively frequently occurring event: coaction was more effective than individual action for moving heavy stones; however, there were no signs of coordination among partners and no improvement through learning. In rhesus groups, instances of coaction were extremely rare, and rates of agonistic interactions were higher than in the Tonkean group. It is suggested that “coproduction” represented an emergent phenomenon resulting from social interactions and, as such, was dependent on the level of interindividual tolerance.