Acid phosphatase levels in pure lymphocytes from normal individuals were determined cytochemically on intact cells and spectrophotometrically on cell extracts. Good correlation was demonstrated between the results obtained with both methods. Biochemical assay showed that a normal range of 7.2 +/- 0.9 and 7.1 +/- 1.0 mMoles per 10(6) lymphocytes was obtained without and with tartrate inhibition, respectively. A significant loss of acid phosphatase level in the extract was found on storage. Seventy-five, 49 and 45 percent of the acid phosphatase activity remained after 3.5, 24, and 48 hours refrigeration at 4 degrees C, with 51 percent and 32 percent after 24 and 48 hours refrigeration at -20 degrees C, respectively. The spectrophotometric assay is less variable than the cytochemical stain. The widely utilized cytochemical method, although less reproducible, allows for evaluation of intracellular distribution of the enzyme in addition to level of activity.