Using semisolid methylcellulose HAT medium selection and non-competitive and competitive indirect enzyme-linked immunosorbent assay, three hybridomas that secreted antibodies for aflatoxin G(1) were selected after fusion of mouse SP2/0 myeloma cells with spleen cells isolated from BALB/c mice that had been immunized with the conjugate of aflatoxin G(1) (AFG(1)) and bovine serum albumin. The aflatoxin-modified protein used to immunize mice was produced chemically by activating aflatoxin G(1) to a 9,10-epoxide derivative, which then covalently bound to the protein. All of these antibodies were found to be specific to AFG(1), and reacted strongly with aflatoxin G(2). These antibodies were designated 1C8, 1C10, and DE7, and had affinities for AFG1 of 5.1 x 10(7), 2.7 x 10(8), and 1.1 x 10(8) liters mol(-1), respectively.