The amino acid sequence of the COOH-terminal CNBr fragment, F3 (residues 130 to 237), of concanavalin A has been established, completing the determination of the covalent structure of this lectin. Analysis of the chemical sequence showed that the distribution of charged residues is generally more dense in the NH2-terminal half of the polypeptide chain than in the COOH-terminal portion and that in the latter region there is a linear stretch composed of many hydrophobic residues. Correlation with x-ray crystallographic results indicates that the hydrophobic region is located in the interior of the molecule, and that it forms a part of a deep cavity which is the binding site for the inhibitor, beta-(o-iodophenyl)-D-glucopyranoside. In conjunction with the three-dimensional structure, the amino acid sequence reported here provides new data for analysis of variables involved in predicting the three-dimensional folding of proteins from the primary structure. The sequence of concanavalin A is the first determined for a lectin and it serves as a reference structure for comparisons with other lectins.