Investigations were made on the excretion of pyridoxine plus pyridoxamine, pyridoxal and 4-pyridoxic acid in the urine of patients with various diseases as well as healthy infants, children, and adults during 24 hour with and without the administration of pyridoxine. The results showed that a considerable diferrence was recognized in the urinary excretion of B_6 vitamins and their metabolite among individuals and days as well as a seasonal fructuation, showing a tendency to decrease in hot season. The maximum excretion of pyridoxine plus pyridoxamine in urine was recognized 1 hour after the administration of pyridoxine, and those of pyridoxal and pyridoxic acid followed the former, and their excretion returned to normal in the same order. Abnormal vitamin B_6 metabolism was observed in the children who suffered from systemic eczema, asthma, apparent ariboflavinosis, acute nephritis or nephrosis.