The specificity of five mouse monoclonal antibodies to okadaic acid was studied for use in an enzyme-linked immunosorbent assay of okadaic acid and its analogs. OA8-2 and OA22-22 antibodies (IgG2a-kappa), which bind more strongly to dinophysistoxin-1 and 7-O-palmitoyl-dinophysistoxin-1 than to okaic acid or 7-O-palmitoyl-okadaic acid in 50% aqueous methanol, were useful in the detection of dinophysistoxins-1 and -3. OA10-8 (IgG1-kappa), which binds more strongly to 7-O-palmitoyl-okadaic acid and 7-O-palmitoyl-dinophysistoxin-1 than to okadaic or dinophysistoxin-1 in 50% aqueous methanol, was useful in the detection of dinophysistoxin-3. OA423-3 (IgG1-kappa), which binds weakly to dinophysistoxin-1 and 7-O-palmitoyl-dinophysistoxin-1 in 20% aqueous methanol, was useful in the selective detection of okadaic acid. OA958-2 (IgG1-kappa), which binds with equal strength to each of the four toxins in methanol, was useful in the detection of all okadaic acid analogs, and the minimum detectable concentration was 30 ng/ml. OA423-3 and OA958-2 retained their binding ability in 50% acetone, ethyl ether, or benzene in methanol.