Clinical course of Case 1. Bosentan monotherapy was started in May 2008 at 125mg/day, and after a month, liver function abnormalities appeared. Abnormal results of liver function tests were normalized within a month after the discontinuation of bosentan. In February 2009, combination therapy of bosentan (62.5mg/day) and ursodeoxycholic acid (300mg/day) was started. There were no subsequent abnormal results of liver function tests, and the dose of both ursodeoxycholic acid and bosentan were increased to 600mg/day and 125mg/day from March 2011, respectively. No abnormal results of liver function tests were observed. Abbreviations: ALP, alkaline phosphatase; ALT, alanine aminotransferase; GGT, gamma-glutamyltransferase.