With the purpose to ascertain clinical significance of urinary mesobilirubinogen in various disease, the author studied by means of the mesobiliviolin reaction changes of mesobilirubinogen contents in the urine of those patients suffering from hepatitis, liver cirrhosis, lung tuberculosis, constipation, and others, who proved positive to the urobilinogen reaction. Simultaneously their liver functions were examined. The results of this study are summarized as follows. 1. It is best to determine the mesobiliviolin reaction six minutes after boiling, and the isolation of mesobiliviolin can be achieved most adequately by column chromatography. By this method there will be yielded some substances other than mesobiliviolin as the by-products. 2. The positive rate to the mesobiliviolin reaction is 50 % in liver cirrhosis, 40 % in serum hepatitis, and 11.8 % in chronic hepatitis, indicating that the severer the injury of liver parenchyma, the higher is the positive rate. In the case of normal persons and those with constipation the reaction is negative. In addition, no positive case can be recognized in those cases with less than 0.40mg/dl of urobilinogen. 3. There cannot be observed any proportional relation between the urobilinogen concentration and the mesobilirubinogen content. 4. In those cases proved to be positive to the mesobiliviolin reaction the positive rate of various examinations on liver function was 50-62.5%, whereas those positive to urobilinogen it was 15.5%-25.8%. 5. It is assumed that the positivity to urinary mesobilirubinogen reaction is of a great importance for determining the disorder in the liver function.