Non-alcoholic steatosis hepatitis and fatty cirrhosis represents an unfamiliar liver disease of yet unknown etiology, which is usually indistinguishable from alcoholic lesions by histological criteria. For the affected patients this means automatically the inappropriate assumption of hidden alcohol abuse. Out of 1467 liver biopsies during 1979 to 1982 we selected 25 patients (group I), who either denied alcohol intake or reported negligible consumption. None of them had taken steatogenous drugs or had been treated by jejuno-ileal bypass operation for morbid obesity. Nevertheless, in all cases liver biopsy demonstrated changes that were thought to be characteristic of alcoholic liver disease. This group was compared with an additional series of 25 patients (group II, selected out of 342 alcoholics), who admitted to a mean daily alcohol ingestion of 145 +/- 37 g. According to body weight, sex ratio, estimated degree of hepatocellular fat deposition and relation of steatosis hepatitis (n = 15) to fatty cirrhosis (n = 12) there were no differences between both groups. In contrast to the alcoholics (group II) significantly lower (p less than 0.001) values of serum gamma-glutamyltransferase (127 +/- 138 vs 669 +/- 588 U/l) and mean corpuscular erythrocyte volume (89 +/- 4,7 vs 102 +/- 7,8 fl) occurred among the abstinent patients (group I). However, the considerable overlap of measured values argued against a sufficiently discriminative function of both parameters. On the other hand, the serum SGOT/SGPT ratio (I: 1,0 +/- 0,4 vs II: 3,5 +/- 1,4) as well as the serum immunoglobulin-index IgG/IgA (I: 5,6 +/- 2,1 vs II: 2,7 +/- 0,7) allowed a more than 90% separation between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)