Recent technologic advances now permit instant gait analysis, making clinical use of the gait laboratory feasible. In this study, the ambulation of two amputees with hydraulic knee prostheses is evaluated by measuring ground reactive forces and by tracking the motion of lights attached to limb segments. A PDP 11/34 minicomputer records, integrates, and processes data received from an 8-channel force plate and from two high-speed solid-state array cameras. Information in the form of ground reactive forces, angular displacements and angular velocities of normal and prosthetic limbs is displayed on a monitor and graphed on an X-Y plotter. Adjustments are made immediately to the hydraulic mechanism so that optimal function of the prosthetic equipment can be objectively determined.