Continuous feed activated sludge systems provide excellent facilities for evaluating detergent biodegradability only when the environmental conditions can be rigidly controlled. Degradation is rapid in such a system, and because of the microorganisms and environment used, the rate and extent should closely approximate detergent decomposition in many municipal waste disposal plants. The design and operation of such a continuous feed activated sludge unit are described, and observed detergent degradation patterns are reported.