The Kinetic Communicator (KINCOM), a microcomputer controlled, hydraulically driven device for the test, measurement, and rehabilitation of human joint function, was tested for the reliability and validity of its operating systems. Testing focused on the three primary functions of the KINCOM: lever arm position, lever arm velocity, and force measuring systems. Measurements of the functions were made via external devices and were compared to measurements simultaneously made by the KINCOM system. Tests were performed for both static and dynamic operation of the unit. Force measurements averaged a difference of 3.2% or less, lever arm speed was within 1.5% of the target speed in all cases, and no difference was found in position measurement. These discrepancies were felt to be due to calibration error and were not considered an indication of inaccuracy in the KINCOM system.