Large amounts of bile acid sulfate were found in the urine of patients with hepatobiliary diseases. In patients with acute hepatitis, daily excretion of bile acid into urine was 68.24 plus or minus 51.80 mumoles per day, and the percentage of sulfated bile acid was 83.4 plus or minus 16.7%. In patients with chronic hepatitis and cirrhosis, a slight increase of urinary bile acid was observed (2.89 plus or minus 2.69 and 5.27 plus or minus 4.28 mumoles per day, respectively), and the percentage of sulfated bile acid was 73.9 plus or minus 28.6 and 44.6 plus or minus 30.4%, respectively. In patients with obstructive jaundice, a moderate increase of urinary bile acid was found (32.62 plus or minus 18.35 mumoles per day), and the percentage of sulfated bile acid was 58.3 plus or minus 22.6%. In patients with hepatobiliary diseases, the elevation of both levels of sulfated and nonsulfated bile acids in serum was observed. The percentage of sulfated bile acid was 9% in normal serum, and varied from zero to 82.8% in pathological sera. A remarkable increase of sulfated bile acid was found in patients with obstructive juandice and acute hepatitis, while a slight elevation was found in patients with chronic hepatitis and cirrhosis. Sulfated bile acid in bile was nonexistent or below 0.5% of total bile acid. According to these findings, the increased bile acid in serum of patients with hepatobiliary diseases might be more easily excreted into the urine as sulfated bile acid.