Isoenzyme 1 of lactate dehydrogenase (LD1) was measured by an immunoprecipitation method. The antibody to M subunit of LD was added to the patient’s serum and incubated for 5 min,at room temperature. The ratio of serum to antibody was 10:1.After incubation,a saturated ammonium sulphate solution was added with the same volume as serum. Then,centrifuged to precipitate all M-containing isoenzyme (LD2—LD5) as insoluble antigen-antibody complex. Determined the residual activity of LD in supernatant fluid. The relationship Between the LD activity and absorbance was linear up to 618U/L. Within-run coefficient of variation (CVs) of two samples were 3.8% and 4.7%.Day-to-day coefficient of variation (CVs) was 7.0%.The correlation of immunoprecipitation method and electrophoretic procedure were cinsistent (n=22, r=0.976).Reference values for total LD and LD1 were 102.3±16.4U/L and 23 .7±4.4U/L respectively. The ratio of LD1 to total LD was 23.1±3.9%.The advantages of immunoprecipitation method were:high specificity. good precision and linearity. easy operation. Immunoprecipitation method was very suitable for measuring LD1 and could adaptable to the automatic analyzer.