The amino acid sequence of the L-arabinose-binding protein of Escherichia coli B/r was determined by sequenator analyses of reduced and S-pyridylethylated L-arabinose-binding protein and fragments derived by chemical and enzymatic cleavage of the native protein. The fragments were the products of cleavage by cyanogen bromide. BNPS-skatole, hydroxylamine, mild acid hydrolysis, limited trypsin digestion, chymotrypsin subdigestion, and subdigestion with Staphylococcus aureus protease V8. The COOH-terminal sequence was determined using bovine carboxypeptidases A and B and amino acid analyses. The L-arabinose-binding protein was determined to contain 306 amino acid residues, the sequence of which is presented below.