In this study, serum Zn2+ content was determined by a new enzymatic method. The method depends on the reactivation of apocarbonic anhydrase proportional to the Zn2+ content of the sample. Carbonic anhydrase was purified from bovine erythrocytes by affinity chromatography. The Zn2+ in its structure was removed by dialysis against pyridine 2,6-dicarboxylic acid, resulting in a pure apoenzyme with a yield of 100%. The activity of the enzyme was determined by its esterase effect on 4-nitrophenyl acetate. Zn2+ levels were determined in the serum samples obtained from 100 healthy subjects, 10 patients with cirrhosis, 12 diabetic patients and 15 patients with chronic renal failure by this enzymatic method and by atomic absorption for comparison. There was a good correlation between the two methods in all patients and controls and intraassay CV% was 2.4 and 4.2 for enzymatic and atomic absorption methods, respectively and interassay CV% as 3.9 and 6.1 respectively.