A prototype semi-active suspension system using fast, continuously variable, electrorheological (ER) shock absorbers was installed on a demonstration vehicle. The shock absorbers had no moving parts other than the piston/rod moving relative to the body of the device. Damping was obtained by controller/power supplies individually applying voltages to the four shock absorbers as determined by a modified sky-hook algorithm which included control of heave, pitch and roll body motions. The damping parameters could be adjusted for tuning ride and handling characteristics. The system was designed to respond in less than 10 ms with an average power requirement less than 40 W for normal road surfaces and handling. Data are presented that document the performance of the demonstration vehicle. Within the optimal temperature range of the system, the suspension performed as designed.