A screening method has been developed for detecting sulfamethazine(SMZ) contamination of meat or feeds by using horseradish pero×idase (HRP) labeled protein A (Prot A-HRP)and an indirect competitive enzyme-linked immunosorbent assay(ELISA). The assay is based on competitive binding of guinea pig anti-SMZ with SMZ in sample and SMZ-gelatin con$lt;jugate(SMZ.GEL) followed by the uptake of prot A-HR,P onto polystyrene microwell plate coated with SMZ.GEL. Percent binding B/Bo × 100) was calculated from the absorbance in the absence (BO) and presence (B) of SMZ. By the sandard curve prepared by plotting log(SMZ) vs percent binding of each lmown reference solution, the detection limit was 1.0 ppb or leas. Cross reaction with sulfadimethoxine, sulfaguaniding, sulfamerazine, sulfamthoaypyridazine, sulfanilamide, aulfisomidine and aulfisoxazole were not observed. But sulfamerazine crosareacted in the test. The EC-50 value (concentration causing 50% inhibition of color development compared with blank) of sulfamerazine was 2.0 ppm. Further quality control will make the ELISA system ideal for the detection of SMZ in meat or feeds.