Natural killer (NK) cell activity against two types of target cells was found to be low in patients with inactive alcoholic cirrhosis (AC). This defect was significantly more pronounced in AC patients with severe malnutrition than in those with mild or moderate malnutrition. This was not due to modifications of the kinetics of NK activity. The sera from AC patients had no inhibitory effect on the NK activity of normal subjects. Lymphocytes and macrophages from AC patients did not exert major suppressive effect on the NK activity of normal subjects. Interferon boosted the NK activity of cells from AC patients, but to a lesser degree than cells from normal controls. The findings show that a deficit of NK activity is clearly associated with inactive AC. This seems to be another consequence of AC on cellular immunity, and might be related to the protein calorie malnutrition often present in AC.