Monoclonal antibodies were raised against the lectin of Helix pomatia (HPL). Besides antibodies bearing the more common gamma and kappa chains, antibodies with alpha, mu and lambda 2 chains were elicited. The anti-HPL antibodies are expected to be useful in studies on HPL biogenesis and HPL substructure and in studies concerned with the binding of HPL to cell surfaces. Binding of carbohydrates to HPL impaired the binding of anti-HPL antibodies. One to 3 mM GalNAc inhibited HPL-binding in two out of nine antibodies. None of the antibodies bound in the presence of micrograms per ml of the polyvalent blood group A-substance from hog stomach. Similarly, all anti-HPL antibodies were prevented from binding if non-inhibitory concentrations of A-substance were supplemented with GalNAc. Lectins from Helix aspersa (HAL) and Helix lucorum (HLL) differed from HPL in antigenic properties. Only one anti-HPL antibody each bound these lectins as well as HPL. Binding of lectins of Cepaea and Rapana was scarcely detectable. Most of the anti-HPL antibodies and the multivalent HPL-antigens formed precipitation lines in double diffusion tests. At least two antibodies (IgMs) did so with HLL but none with HAL. The possibility that antibodies were selected because of unknown interactions between HPL and the carbohydrate moieties of certain fractions of antibodies was excluded by raising the antibodies in the presence of tunicamycin to inhibit N-glycosylation.