Highly sensitive, specific immunoenzymatic assay for human alpha 2-macroglobulin was developed using solid phase 'sandwich' procedure. The immunoenzymatic assay developed involved the following steps: 1. preparation of highly purified alpha 2-macroglobulin, 2. production of monospecific antiserum against the protein, 3. preparation of the immunoenzymatic assay system components--isolation of antibodies against alpha 2-macroglobulin, conjugation of these antibodies with horseradish peroxidase, standardization of the assay. Sensitivity of the assay was 31,25 ng/ml, duration of the analysis--3 hrs. The assay enabled to estimate the proteinase inhibitor in various human biological fluids. Content of alpha 2-macroglobulin in blood plasma, urine and tears was estimated in normal and some pathological states.