This presentation describes effects of oral tryptophan loading (5.0 g DL) on tryptophan metabolism in healthy subjects (n = 10) and persons with progressive scleroderma. N1-methylnicotinamide (N1MN), 3-hydroxyanthranilic acid (3 HAA), kynurine (KN), tryptamin (TA), xantheurenic acid (XA) were determinated. Alterations of tryptophan metabolism were evaluated by 24 h urinary excretions of the following metabolites: 5-hydroxy indolacetic acid (5 HAA) and indole-3-acetic acid (IAA). The pathological pathways were discussed, especially the way and influence of serotonine.