The higher nervous system reactions of rhesus monkeys to the head-down tilt (HDT, 28 d, -5 degrees) and preventive centrifugation were evaluated with the use of a computerized psychological testing system (PTS). Prior to HDT, the primates elaborated conditioned instrumental food-obtaining reflexes by playing computer games. Drilled to perform PTS tests to the best of their ability, the animals were to fulfill two PTS tests of increasing complexity in HDT. Test results were used to determine the dynamics of primates' cognitive function and the psychological state. The investigation consisted of two series with two groups of monkeys in each series. Twelve animals of each group (10 had skill in performing the PTS tests) were distributed into 2 subgroups. Every other day one of the subgroups was exposed to centrifugation at 1 to 2.5 g. In the first series, 10 monkeys worked on the simplest test, i.e. spotting a static object. All animals showed interest in the computer game, and played a lot and successfully during HDT. In the second series, the animals were challenged with a more difficult test of following a moving object with the cursor. Based on the analysis of experimental data, a significant variability in achievement and emotional behavior of the primates should be attributed to different types of the nervous system.