A semi quantitative radiometric assay for non-specific opsonization using 3H-UdR was discribed in this paper. The opsonin activity was generated by incubating yeast with normal polymorphon-uclear leukocytes in medium containing 5%human serum. Some factors influencing the test’s result and optimal test condition selected in this paper were discussed. The opsonizations by sera from 43 of normal adults and 10 of patients with fulminant and subacute liver failure have been examined in this study. The data showed that the opsonin indices of patients mentioned above were much lo-wer(0.6 + 0.8) than those(4. 1+1.3)of normal samples (p/0.001). It suggested that a significant deficiency of opsonization was found in the sera from patients with fulminant and subacute liver failure.