In search of a method to increase the validity of experimental data and simultaneously counteract the negative consequences of restricted laboratory environments, a pilot study was run with three rhesus monkeys (Macaca mulatta), which were trained and tested with a laboratory-type task in the animal housing facility. The testing apparatus was made available to individual animals 24 hours a day at their living cage and was connected to a computer that controlled the test and the distribution of regular monkey chow as reward. The animals were thus able to work whenever they wanted, for whatever period of time they chose, in their accustomed home environment. Besides furnishing data on the distribution of activity and performance over extended periods of time, the study provided more data than those obtained previously when animals were tested each day for only a limited time in an isolated test chamber. It was also found that the self-initiated manipulatory activity required by the test considerably reduced the number of motor stereotypies. Thus, testing animals within the housing facility was profitable for the investigators and beneficial for the animals.