1. Leopard frog (Rana pipiens) erythrocytes are agglutinated by the plant lectins concanavalin A and phytohemagglutinin. 2. Concanavalin A hemagglutination can be specifically inhibited by the sugars mannose, glucose, arabohexulose, alpha-methyl-D-mannopyranoside, N-acetyl-D-glucosamine, maltose, sucrose, trehalose and melezitose. 3. Sugars inhibiting concanavalin A hemagglutination are structurally composed of alpha-D-glucopyranosyl, alpha-D-mannopyranosyl or beta-D-fructofuranosyl residues with the same hydroxyl groups at carbons 3, 4 and 6. 4. Phytohemagglutinin hemagglutination can only be inhibited by the sugar N-acetyl-D-galactosamine. 5. Sugar inhibition of concanavalin A and phytohemagglutinin leopard frog erythrocyte agglutination is the same as that observed in many mammalian species.