Background. Controversies exist about the association between significant bacteriuria and primary biliary cirrhosis. There is evidence suggesting that infections by Gram negative bacteria may be implicated in the pathogenesis of this liver disease. Aim. To compare the incidence of bacteriuria in patients with primary biliary cirrhosis and those with autoimmune chronic hepatitis. Patients and methods. Twenty women with primary biliary cirrhosis and twenty three female patients with autoimmune chronic hepatitis were prospectively studied by routine bacteriological cultures of midstream urine specimens. Samples were obtained at three months intervals or when patients complained of symptoms suggesting urinary tract infection. Significant bacteriuria was defined as the growth of > 10(5) organisms/ml in pure culture. Results. During 8 +/- 1 months of follow up. 60 urine samples from patients with primary biliary cirrhosis and 73 from autoimmune hepatitis cases were tested. Twenty one samples of patients with primary biliary cirrhosis (35%) were positive for significant bacteriuria compared with 7 from women with autoimmune hepatitis (9%) p < 0. 01. In the follow up, ten patients with primary biliary cirrhosis (50%) and six with autoimmune hepatitis (26%) developed at least one episode of significant bacteriuria. Conclusion. These results suggest that female patients with primary biliary cirrhosis are in higher risk of significant bacteriuria than women with autoimmune hepatitis. Prospective studies evaluating the effects of long-term antibiotic therapy on cholestasis parameters In primary biliary cirrhosis are deserved.