Abstract: 1. Examination of the riboflavin content of the 24 hour urine and blood of tuberculosis patients failed to show a significant statistical difference among the mild, moderately severe and severe cases. Ariboflavinosis could not be confirmed.2. Excretion of riboflavin in the urine following administration of the vitamin varied individually and the vitamin metabolism was found to differ in each individual.3. Cases were found among the tuberculosis patients in which an abnormally large quantity of riboflavin was continuously excreted in the urine. The vitamin excretion in the patient differed from that of tuberculosis patients in general. This large excretion ceased on administration of Aureomycin.