The aim of this study was to evaluate the diagnostic usefulness of percutaneous liver biopsy and screening for hepatitis C virus antibodies with 1st and 2nd generation ELISA in asymptomatic blood donors with persistent (> 1 year) and moderate elevation (> 1.5 times the upper limit of normal) of serum alanine aminotransferase. The diagnosis was established from clinical, biological and ultrasound data before biopsies were obtained, then compared to the histological diagnosis. Thirty one of 56 blood donors who satisfied the preceding criteria accepted liver biopsy and were subsequently included in the study. An accurate diagnosis was proposed before biopsy in 20 cases. This was in agreement with the histological results in 19 cases but in 2 of these, unexpected lobular hepatitis was associated with the expected steatosis. Positive hepatitis C virus tests corresponded to chronic hepatitis in all cases (n = 5). No accurate diagnosis could be proposed in the 11 remaining cases owing to the lack of evidence of any etiology (n = 4) or because several potential etiologies were possible for the same subject (n = 7). Histological diagnoses were: isolated steatosis (n = 12), steatosis associated with lobular hepatitis (n = 7) or with chronic persistent hepatitis (n = 1), chronic active (n = 2) or chronic persistent hepatitis (n = 3), alcoholic hepatitis (n = 2), hemochromatosis (n = 1), and normal liver (n = 3). Liver biopsy is essential to the accurate etiological diagnosis of persistent and moderate elevation of aminotransferases despite hepatitis virus C tests which are associated with the correct diagnosis of chronic hepatitis in 16% of cases.(ABSTRACT TRUNCATED AT 250 WORDS)