Crude extracts of Cicer arietinum seedlings contain enzymes that mediate the oxidation of tryptophan. The most active is formylase followed by tryptophan oxygenase and kynureninase. Tryptophan is also utilized for the synthesis of indolyl-3-acetic acid. The stimulation of tryptophan oxygenase in seedlings incubated in presnece of indolyl-3-acetic acid has been shown by specific labelling of haem moeity and the apoenzyme not to involve de novo synthesis.