Bullfrogs injected with dinitrophenyl keyhole limpet hemocyanin (DNP-KLH) in complete Freund's adjuvant produced precipitating anti-DNP antibody with characteristics different from that produced by frogs immunized against DNP-Salmonella in saline. The antibody from animals injected with DNP-KLH sedimented as a 7S protein on sucrose density gradients and gave precipitin curves similar to the precipitin curve of mammalian 7S-IgG except for the lack of 100% precipitability of the antigen over most of the frog curve. DNP-Salmonella induced antibody which sedimented as a macroglobulin and was distinguished from the light antibody induced by DNP-KLH by radioimmunoelectrophoresis. The precipitin curve for this immunoglobulin and the persistence of high titers 1 year after a single injection suggest that the immunoglobulin is IgM.