This study was concerned with the assessment of the effects of two stress conditions on 16 basic dimensions of perceptual-motor performance. Subjects were tested under conditions of heat stress (86° F effective temperature for a period of six hours) and prolonged activity (24-hour continuous activity, with two 2-hour rest periods). In general, perceptual-motor performance levels were well maintained under these stress conditions. Under heat stress, six tests showed facilitation, while two showed degradation of performance. Facilitation under heat stress was accounted for in terms of arousal theory under which activities requiring minimal information processing and involving simple motor reactions appear to benefit from the alerting component of arousal. Under prolonged activity, two tasks showed facilitation and one showed degradation in performance. These effects were explained in terms of requirements specific to the individual tasks. In general, there was essentially no change in performance effectiveness during the 24-hour period of prolonged activity. Under heat stress, oral temperature and pulse rate increased significantly, lending support to the inference of increased arousal. Under prolonged activity, no change was noted in oral temperature, pulse rate, or blood pressure. This was consistent with the general lack of change in the performance measures indicating this level of stress was well tolerated. To an extent compatible with the intensity of the stress conditions which were used, the basic dimensions of perceptual-motor performance appear differentially sensitive to stress. The results offer insight as to the mechanisms whereby stresses such as were used in this study affect more complex operational performance. The findings of this investigation demonstrate the usefulness of the integrated measurement system as a device for the study of human performance.