Present information about the behavior of the different lymphoid subsets in alcoholic hepatitis (AH), including cells displaying cytotoxic activity, is scanty and contradictory. The aim of this study was to gain further insight into knowledge of the immunological abnormalities involved in AH and the possible role of ethanol (EtOH) consumption in these changes. We analyzed the distribution of a wide range of peripheral blood (PB) lymphoid subsets, both during active EtOH intake and after a 3-month withdrawal period, using multiple stainings with monoclonal antibodies and flow cytometry, as well as natural killer (NK) cytotoxic activity. AH patients entering the study were selected strictly; only those undergoing their first episode of AH with no other lesions a liver biopsy were enrolled. Regarding the alcohol intake period, the most striking finding was a significant increase of the absolute number of PB T cells affecting both CD4(+) and CD8(+) lymphocytes. These changes were associated with a higher expression of T-cell activation antigens, such as HLA DR and CD11c. Simultaneously, a significant increase In both NK cells (CD3(-)/ CD56(+)) and the cytotoxic T cells coexpressing the CD3 and the CD56 molecules together with an increased NK cytotoxic activity were observed. By contrast, the CD19(+)/CD5(+) B-cell subset was significantly decreased. No significant changes were observed with EtOH withdrawal except in CD5(+) B lymphocytes, which returned to normal values. Our results show that, in AH patients, a significant expansion of both activated T cells and NK lymphocytes occurs in the PB, which is associated with an increased NK cytotoxic activity. interestingly these abnormalities persist during the withdrawal period.