Plasma met-enkephalin immunoreactive material (ME-IR) concentration was measured in 175 aged subjects (68 males, 107 females). Heavy drinking (1 liter of red or white wine a day, equivalent roughly to greater than 110 g ethanol) was associated with reduced ME-IR concentrations. On the other hand, no correlation was found between plasma ME-IR and other parameters such as blood pressure, age or body weight. These data favor the hypothesis of an involvement of ME-IR in the mechanisms of ethanol action.