Urinary xanthurenic and kynurenic acid levels were measured in five patients while they were receiving 50 mg and 100 mg of pyridoxine. The levels of tryptophane metabolite decreased progressively as the dose was increased but remained above basal levels. There was marked clinical improvement in these patients while receiving the higher dose only. The double-blind study with 76 asthmatic children followed for five months indicated significant improvement in asthma following pyridoxine therapy (200 mg daily) and reduction in dosage of bronchodilators and cortisone. The data suggest that these children with severe bronchial asthma had a metabolic block in tryptophane metabolism, which was benefitted by long-term treatment with large doses of pyridoxine.