The effect of chronic ethanol consumption on plasma and erythrocyte membrane lipids were studied in rats fed a liquid diet containing ethanol for 4 weeks and intubated with the same diet 90 min prior to killing. Control animals underwent the same treatment, except that their liquid diet did not contain ethanol, but an isocaloric amount of carbohydrates. Plasma total cholesterol, free (unesterified) cholesterol and HDL cholesterol were higher in ethanol-fed animals than in controls. Phospholipids were also higher in the plasma of ethanol-fed animals when compared to controls so that the plasma cholesterol/phospholipid ratio (Ch/PL ratio) of the two groups did not differ significantly, regardless of the cholesterol fraction considered. Experimental and control animals did not differ either in the Ch/PL ratio of their erythrocyte membranes. In view of the fact that it has been suggested that the factor determining the direction of the cholesterol exchanges between plasma and erythrocyte membranes is the equilibrium between their respective Ch/PL ratios, these results are interpreted as being compatible with the hypothesis that the effect of chronic ethanol intake on erythrocyte membrane lipids is mediated through changes in plasma lipids.