Information compiled by automatic Edman degradation of Streptomyces griseus trypsin coupled with previous data has permitted the assignment of the first 36 residues at the NH2 terminus of the protein. Cyanogen bromide cleavage at the three methionine residues followed or preceded by reduction and aminoethylation resulted in the production of four fragments, Cnl to Cn4, which were separated by gel filtration on Sephadex G-50 or G-75. Fragments CN4 (15 RESIDUES) AND Cn3 (5 residues) were shown to be derived from the NH2 terminus of the protein while Cn2 (47 residues and devoid of homoserine) was from the COOH terminus. The arrangement of the fragments was thus Cn4-Cn3-Cn1-Cn2. Automatic Edman degradation in the sequenator coupled with peptides derived from alpha-lytic protease and chymotryptic digestion and from the peptic and tryptic peptides previously elucidated have permitted the sequence determination of fragments Cn1 and Cn2 and therefore of the whole protein. These studies show that extensive regions of identity or similarity exist between Streptomyces griseus trypsin and bovine trypsin. These include the NH2-terminal four residues, the sequences near histidine-57 (chymotrypsinogen A numbering system), aspartic acid-102, aspartic acid-189, and serine-195, the regions of the three disulfide bridges, and the COOH-terminal end (residues 225-229) of the proteins. When aligned to maximize homology the identity of residues is 34%. This identity is increased to 54% when only those residues classified as internal by Stroud et al. (Stroud, R. M., Kay, L. M., and Dickerson, R. E. (1971) Cold Spring Harbor Symp. Quant. Biol. 36, 125) are considered. These results indicate that the folding of the polypeptide chains of the two enzymes is very similar and are in agreement with the very similar enzymic, chemical, and physical properties of the two enzymes.