Cytochrome P-450 (CP-450) is one of the three components of the liver microsomal enzyme system which hydroxylates fatty acids, hydrocarbons and a variety of drugs and other foreign compounds. Female Balb/c mice were immunized with purified polychlorinated biphenyl (PCB) – induced CP-450 LMII. The spleen cells derived from immunized mice were fused with SP2 myeloma cells using polyethylene glycol (PEG 3500). The hybrid cells were selected by hypoxanthine-aminopterin-thymidine (HAT) medium and the culture fluid were screened by enzyme-linked immunosorbent assay to CP450 LMII. The hybrid cells(×107) were inoculated into intraperitoneal cavity of Balb/c mice for the purpose of production of ascetic fluids. Monoclonal antibody (Mab) was purified from ascitic fluid by DEAE cellulose ion exchange chromatography and I¹²⁵ labeled Mab was also confirmed by autoradiography and SDS-polyacrylamide gel electrophoresis (MW:55,000 and 110,000)