Hemolysis in serum specimens is commonplace. This study examines the effect of hemolysis on results of selected chemical assays. Hemolysis was simulated by adding hemolysate to serum to give hemoglobin concentrations of 90 to 2800 mg/liter and a rating by technologists of 0 to 4 + hemolyzed. The effect of hemolysis on values for some serum constituents, particularly acid phosphatase and creatine kinase, was shown to be method dependent. Not unexpectedly, hemolysis most affects results for lactate dehydrogenase.