Antiserum, specific to rat liver microsomal epoxide hydrolase, was produced. Three methods for quantitative estimation of the epoxide hydrolase, base on the principle of antigen-antiserum immunoprecipitation, were used: electroimmune analysis by Laurell, radial immunodiffusion, enzyme-linked immunoassay. Distinct correlation between specific enzyme activity and its content in microsomal preparation was demonstrated using a simple and stable procedure of radial immunodiffusion. In the enzyme-linked assay conjugate of protein A with alkaline phosphate served as the secondary antibody. Sensitivity of the procedure described was about 1,000-fold higher as compared with radial immunodiffusion method.