Large amounts of an esterase that migrated to the γ-globulin region (γ-esterase) upon cellulose acetate electrophoresis were excreted in the urine from patients with renal diseases. The γ-esterase localized in the renal tubules of the kidney in patients with renal tubular diseases was purified and shown to be identical with the urinary esterase that migrated to the γ-globulin region by immunological studies. The esterase has a molecular weight of 66000, an optimum pH of 7.5, and pI values of 7.9 and 8.3.