Serum mitochondrial and total aspartate aminotransferase activity was quantified by a characterized immunochemical method in 126 subjects, 44 healthy controls and 82 chronic alcoholics (51 outpatients and 31 monitored through 15 days). The monitored alcoholics were divided into actual abstinents (n = 21) and drinkers (n = 10) by blood ethanol concentration performed daily. The aims of the present study were: (a) to compare the diagnostic diagnostic usefulness of the mitochondrial isoenzyme and the mitochondrial/total aspartate aminotransferase ratio to detect problematic drinkers; (b) to evaluate the suitability of these indices to monitor abstinence, a difficulty not yet solved in the clinical management of alcoholics. The results demonstrated the mitochondrial isoenzyme to be more suitable to discriminate between controls and alcoholics (Kruskal and Wallis ANOVA, Bonferroni test, P < 10(-5) and mostly between actual drinkers and other alcoholics (P < 0.041). So acute alcohol consumption may be a significant, suggestive and until now inadequately examined factor in evaluating the suitability of mAST as a marker. The results, showing that mAST peaks quickly appear in the presence of a new alcohol intake, should indicate mAST as a possible marker of acute alcohol intake useful in checking self-claimed abstinence.