New Zealand White rabbits immunized with covalent conjugates prepared from polylysine and the O-carboxymethyloxime derivatives of either aflatoxin B1 (AFB1) or an analogue, 5,7-dimethoxycyclopentenon (2,3-c)coumarin, produced antibodies that bind 3H-AFB1. The specificities of the antisera with respect to aflatoxins B2, B2a, G1, G2, Q1, P1, and some other structurally related compounds were determined. Radioimmunoassays that can detect levels as low as 0.27 pmoles (0.06 ng) of AFB1 were used to analyze serum, urine, and crude extracts of corn and peanut butter supplemented with aflatoxin. In the foodstuffs, as little as 1 µg AFB1/kg was measured. The immunoassay was at least as sensitive and specific as other available analytic methods, but did not require the purification of samples by chromatography before analysis. The technique may be particularly...