The aim of this study was to define factors predictive of the onset of the terminal phase, defined by hyperbilirubinemia or the occurrence of a severe clinical complication, in patients with primary biliary cirrhosis treated with ursodeoxycholic acid. The 97 primary biliary cirrhosis patients in this study participated in a 2-yr clinical trial. Four of the 49 patients treated with ursodeoxycholic acid (13 to 15 mg/kg/day) entered the terminal phase of the disease, compared with 9 of the 48 patients assigned to placebo. In addition to clinical, conventional biological and histological parameters, we analyzed three serum markers of connective tissue components-type III procollagen aminoterminal peptide, hyaluronic acid and laminin. In the ursodeoxycholic acid-treated group, hyaluronic acid, type III procollagen aminoterminal peptide, bilirubin and splenomegaly were the factors most closely associated with entry into the terminal phase of the disease. In multivariate analysis, after adjustment for age, the hyaluronic acid level was the only predictive factor. In the placebo-treated group, the bilirubin level, total bile acid level, Mayo score, type III procollagen aminoterminal peptide, hyaluronic acid, splenomegaly and pruritus were associated with aggravation of disease. In multivariate analysis, high bilirubin level, high type III procollagen aminoterminal peptide or hyaluronic acid levels and low prothrombin time independently implied poor prognosis. In conclusion, when patients with primary biliary cirrhosis are treated with ursodeoxycholic acid, bilirubinemia loses, in part, its predictive value. It is replaced by hyaluronic acid and type III procollagen aminoterminal peptide. This suggests that models used in deciding on the need for liver transplantation require adaptation for patients receiving ursodeoxycholic acid. (Hepatology 1994;19:635–640).