Prostatic acid phosphatase was purified from prostatic fluid. Monospecific antisera to the purified acid phosphatase was then produced in rabbits. When antibody was coupled with acid phosphatase, the enzymatic activity was markedly stabilized against pH and temperature degradation. Both acid phosphatase and rabbit anti acid phosphatase were non specifically coupled to Sepharose-4B using cyanogen bromide. Under these circumstances slight stability occurred when antibody was bound to Sepharose, and then acid phosphatase added to the gel antibody complex. When acid phosphatase was complexed to Sepharose, no stabilization occurred.