Abstract: The invention pertains to an improved heterogeneous enzymeimmunoassay involving the use of a reversibly soluble polymeric substance acting as the support for the antibody. In the direct method the antigen to be detected and an enzyme labeled antigen are bound by antibody which is chemically linked to the soluble polymeric substance. The polymer is rendered insoluble and removed from the test solution. After resolubilization into a solution containing substrate for the enzyme label, the assay for antigen is completed by determination of enzymatic activity. In the indirect method, the antigen to be detected and an enzyme labeled antigen are incubated with a primary antibody unattached to the polymeric substance. After addition of a second antibody which is chemically linked to the polymeric substance, the polymer is rendered insoluble and the assay is performed as in the direct method described above.