<jats:p> Actinomycin synthesis by washed mycelia of <jats:italic>Streptomyces antibioticus</jats:italic> has been conducted in the presence of 3-hydroxy-4-methylanthranilate-( <jats:italic>carboxyl</jats:italic> - <jats:sup>14</jats:sup> C). Incorporation of this compound into actinomycins has been observed, which constitutes further evidence that 3-hydroxy-4-methylanthranilate is an intermediate in actinomycin biosynthesis. The position of the incorporated label has been determined to be within the actinomycin chromophore, and the label appears to be equally distributed between both halves of the chromophore. Incidental to these findings was the observation that the <jats:sup>14</jats:sup> C-labeled actinomycins were subject to rapid reabsorption by the organism with actinomycin V taken up preferentially to actinomycin IV.