We studied the relationship between selected variables of hepatic and pulmonary function in 47 patients with primary biliary cirrhosis, who were participating in a prospective study to assess sequential pulmonary function at yearly intervals. An additional 20 patients with primary biliary cirrhosis, who were liver transplant candidates awaiting transplantation, were studied. None of the 67 patients ever smoked cigarettes. Severity of primary biliary cirrhosis was characterized by histological stage and the Mayo risk score derived from a Cox regression model that used the following variables: serum bilirubin and serum albumin levels, age, prothrombin time and clinical severity of edema. Pulmonary function assessment included key variables describing expiratory airflow (forced expiratory volume in 1 sec divided by forced vital capacity) and efficiency of gas exchange (steady-state diffusing capacity for carbon monoxide). We found a significant relationship between histological stage of primary biliary cirrhosis and steady-state diffusing capacity (p = 0.02) and between the Mayo risk score for disease severity and steady-state diffusing capacity (p = 0.03). Progressive deterioration of steady-state diffusing capacity was associated with increasing severity of primary biliary cirrhosis. No relationship existed between pulmonary function and the presence of sicca complex or Sjögren's syndrome or the clinical manifestations of portal hypertension (e.g., esophageal varices, ascites and splenomegaly). No significant relationship existed between expiratory airflow and severity of primary biliary cirrhosis. We conclude that in patients with primary biliary cirrhosis who have never smoked, a statistically significant relationship exists between the severity of the liver disease and the efficiency of gas exchange measured by steady-state diffusing capacity.(ABSTRACT TRUNCATED AT 250 WORDS)