Excretion of urinary tryptophan metabolites after a 2-gm load of L-tryptophan was measured in patients with occupational bladder cancer (due to exposure to aromatic aimines), and in matched exposed and unexposed control subjects from the same factory. No significant differences were found in mean excretions of kynurenine, acetylkynurenine, hydroxykynurenine, kynurenic acid, xanthurenic acid, indican, anthranilic acid glucuronide, o-aminohippuric acid, or creatinine. Some individual subjects had slight elevations of metabolites so that 2 of 8 patients with bladder cancer present, and 2 of 10 with a diagnosis of bladder cancer but free of disease when studied, were classified as having abnormal tryptophan metabolism. In this regard, their tryptophan metabolism resembled that of male patients from Boston (15% abnormal) rather than that of male patients from Wisconsin (35% abnormal).