In the course of an investigation of puromycin production by Streptomyces alboniger, it was noted that several compounds were produced, in addition to puromycin; and that these compounds interfered with the assay of puromycin in the solvent extract.We determined the nature of these compounds, and identified them as phenylacetamide (I), 3-methylthioacrylamide (II), and 3-methylthiopropionamide (III).C6H5CH2CONH2, (I); CH3SHC=CHCONH2, (II); CH3SCH2CH2CONH2, (III).These products were shown to be the result of metabolism, in that they could not be detected in the corn steep liquor or any other constituent of the complete growth medium. Methionine has been shown 1) to undergo oxidative decarboxylation catalyzed by peroxidase to yield 3-methylthiopropionamide (111), and it is probable that a similar mechanism is responsible for the production of the compound in the fermentation system. Addition of methionine to the fermentation medium increased the production of compounds II and III. It is likely that II arises from III by dehydrogenation. Compound II has been discovered only recently to be produced by Streptomyces ioyaensis, 2) and it is now clear that this compound may be produced by a variety of streptomycetes.Phenylacetamide (I) has been biosynthesized in Actinomyces N-29. 3) It is possible that it arises both in the latter organism and in S. alboniger from phenylalanine via oxidative decarboxylation, in a manner similar to the formation of III from methionine discussed above.