Bleomycin (BLM) and mitomycin C (MMC), potent anticancer agents, were linked covalently to murine monoclonal anti-HLA IgG(1) antibody (H-1) with the use of dextran T-40. Macromomycin (MCR) was coupled to H-1 in the presence of carbodiimide. H-1 alone did not inhihit cell growth. BLM-(H-1) and MMC-(H-1) conjugates showed stronger cytotoxicity to an HLA-bearing cell line than BLM and MMC, respectively. MCR-(H-1) and free MCR showed the same cytotoxicity to HLA-bearing cells, while the conjugate was less toxic than free MCR against cells lacking HLA. These results indicate that BLM-(H-1), MMC-(H-1) and MCR-(H-1) exert antibody-targeting cytotoxicity in vitro.