Studies on the metabolism of tryptophan in Pseudomonas aureofaciens ATCC 15926 revealed different metabolic routes for the L- and D-isomer besides the biosynthetic pathway for pyrrolnitrin synthesis. L-Tryptophan catabolism follows the aromatic route via anthranilic acid. Tryptophan 2,3-dioxygenase were induced by L-tryptophan. Kynureninase and anthranilate 1,2-dioxygenase were induced by L-tryptophan, L-kynurenine and anthranilic acid. Anthranilate 1,2-dioxygenase was absent from a mutant strain of P. aureofaciens ATCC 19526 which produced about 30-fold increased amounts of pyrrolnitrin. The Km values of tryptophan 2,3-dioxygenase and kynureninase did not differ substantially between the two strains. Kynurenine 3-monooxygenase, 3-hydroxyanthranilate 3,4-dioxygenase, tryptophanase and indolyl-3-alkane alpha-hydroxylase activities were not detected. D- and L-tryptophan were converted to indole-3-acetic acid. This additional catabolic pathway was well as tryptophan racemase activity was constitutive and present in both strains.