Abstract 1. 1. Characteristics are given for facilitating 5000-fold purification of prostatic acid phosphatase. 2. 2. A purification starting with 40 human glands is described. 3. 3. Foaming as a purification technique is used and described. A relatively great purification is obtained with foaming. 4. 4. Experiments designed to demonstrate surface inactivation are presented. A study of methods of minimizing denaturation due to glass surface was made, and methods compatible with assay and isolation are presented.