Serum levels of venom antigen were measured using enzyme-linked immunosorbent assay (ELISA) in 38 Russel's viper bite victims before and after administration of 40 ml of monovalent liquid antivenom. Initial serum levels ranged from one with less than 10.0 ng to 290 ng/ml and in one case a level of 75 ng/ml was detected 27 hours after the bite. Serum venom levels after liquid monospecific antivenom therapy indicated that venom clearance was similar in each case to the natural clearance of venom in the absence of antivenom therapy. In one case a venom level of 11.5 ng/ml was detected 66 hours after liquid antivenom therapy whereas in two fatal cases, serum venom levels of 95 ng/ml and 185 ng/ml were detected after the same interval. Failure of complete neutralization of venom is probably the result of loss of potency of antivenom during improper storage. The amount of venom excreted in the urine was not related to initial serum levels.