The supernatants of the homogenates from normal and cancerous human prostatic tissue run on polyacrylamide gel electrophoresis have 2 major electrophoretic bands when stained for prostatic acid phosphatase. The ratios of the electrophoretically distinguishable isoenzymes differ in normal and cancerous tissues. Similar distinctions between isoenzymes in normal and cancerous prostates are observed following column chromatographic separation or isoelectric focusing. The faster electrophoretic band can be separated by diethylaminoethyl cellulose column chromatography or by isoelectric focusing into at least five fractions with different electrophoretic mobilities. We could not find any differences in normal and cancerous tissues among these subfractions of the faster-moving electrophoretic band. Analysis by gel electrophoresis does not show association between these fractions after chromatographic or isoelectric separation of the prostatic acid phosphatase fractions. Quantitative, but no qualitative, differences in prostatic acid phosphatase isozymes occur in normal versus cancerous prostates.