In 90 patients with calcium oxalate urolithiasis an oral tryptophan-loading test with 5 g L-tryptophan was performed and the 24-hour urinary excretion of xanthurenic acid and kynurenine was measured. In 10 cases pathological deviations and an excretion pattern of tryptophan metabolites via kynurenine similar as in the hereditary vitamin-B6-dependent xanthurenic aciduria in homozygous or heterozygous from were found. Correlations between the oxalate excretion and the tryptophan metabolism do not exist. A 2-year therapy with 60 mg vitamin B6 was favourable in patients with an excretion of more than 300 mumol XA after a tryptophan load.