Cholesterol/phospholipids molar ratio and fatty acid composition have been estimated in erythrocyte membrane of 12 patients suffering from nephrotic syndrome and compared to values obtained in 23 normal subjects matched for sex and age. The membrane lipid composition has been correlated with the activity of erythrocyte Li-Na countertransport of the same subjects. The results show a significant increase in cholesterol/phospholipids ratio and total saturated fatty acids when erythrocytes of nephrotic patients are compared to normal erythrocytes, whereas total unsaturated fatty acids were lower in nephrotics (p less than 0.002). Li-Na countertransport was higher in nephrotics (p less than 0.001) and it was positively correlated with the total amount of saturated fatty acids of the erythrocyte membrane (r = +0.451; p less than 0.01). On the contrary, Li-Na countertransport was negatively correlated with the total amount of unsaturated fatty acids (r = -0.468; p less than 0.01).