Thiamine propyl disulfide (TPD) was orally administered in patients with liver disease to measure the main metabolite, 2-hydroxypropyl methyl sulfone (2HPMS), in urine, for the test of liver function. The amount of urinary excretion of 2HPMS decreased in proportion to the degree of severity of liver disease, with intimate correlation with various tests reflecting hepatic reserve function (p less than 0.01). Phenobarbital (PB), one of the inducers of hepatic microsomal drug metabolizing enzymes scarcely influenced the results of this test. In patients with ordinary liver disease without remarkable disturbance of intestinal absorption and renal excretory function, this method appears to be clinically applicable.