This study evaluated the effects of pair-housing on several operant (trained) behaviors in rhesus macaques (Macaca mulatta). Sixteen young, male, individually housed rhesus monkeys (age, 2.5 to 5.5 years) performed a battery of behaviors consisting of motivation (progressive ratio, PR), short-term memory and attention (delayed matching-to-sample, DMTS), color and position discrimination (conditioned position responding, CPR), and learning (incremental repeated acquisition, IRA) tasks. Behavioral assessments occurred 5 days/week, with the PR, IRA, and CPR tasks presented on one test day, and the DMTS task presented on the next test day. Thus, each task was performed two or three days/week. Eight subjects then were pair-housed, while eight age-matched controls remained individually housed. Pair-housed monkeys were separated for behavior testing and feeding but allowed access to each other approximately 20 h/day. The performance of the two groups of monkeys were compared for the 2 months prior to pairing, for a 2-month transition period as the pairs adjusted to the new housing situation, and for a 2-month period after the pairs had been established. Performance of the CPR and IRA tasks did not change over time in either group. For the PR and DMTS tasks, the number of trials completed increased over the course of the study in the controls but not in the pair-housed monkeys. In conclusion, pair-housing monkeys is feasible for studies involving operant behavior testing as a model for a variety of complex brain functions. However, housing condition may affect some test parameters, and this must be taken into consideration during experimental design.