Experiments on the incorportaion of D-and L-[alanine-3-13C, 2-15N) tryptophan into the antibiotic pyrrolitrin in Pseudomonas aurefaciensconfirmed earlierconclusions abou the conversin of L-tryptophan into pyrrolnitrin. They also demonstryated that a fraction ofthe D isomer is incorporta ted without breakage of the 15 N-carbon bond, consisten with the operation of a second pathway from D-tryptophan to pyrrolnitrin. Cell-free experiments confirmed the conversion of 3-(o-aminophenyl) pyrrole into aminopyrrolnitrin but failed to detect enzymatic oxidation of the latter to pyrrolnitrin.