The aralkyl and arylacetyl transferases were purified to homogeneity from bovine kidney by a slight modification of a previous procedure. The M(r) of the arylacetyl transferase was estimated to be 33,500 by SDS/PAGE and that of the aralkyl transferase to be 33,750 by a combination of SDS/PAGE and gel-filtration analysis. N-Terminal-sequence analysis indicated a blocked N-terminus for the arylacetyl transferase and gave the following sequence for the aralkyl transferase: M-F-L-L-Q-G-A-Q-M-L-Q-M-L-E-K. Amino acid analysis revealed differences in composition between the two enzymes. Most notable was the fact that the aralkyl transferase had more methionine and leucine. This difference could be partially accounted for by assuming that the methionine-and-leucine-rich N-terminus was missing from the arylacetyl transferase. Chemical cleavage of the two enzymes at methionine residues using CNBr gave rise to several peptides for each enzyme. N-Terminal-sequence analysis of the 8000-M(r) peptide from the arylacetyl transferase gave a sequence with 69% similarity to the 9000-M(r) peptide from the aralkyl transferase. This was taken to indicate a common origin for the two enzymes.