We observed the effect of 10% intralipid on the membrane fluidity of lymphocytes by means of fluorescent polarization measurement. After in vitro incubation with intralipid in concentration 0, 10, 20mg/ml, the lymphocytes from healthy adult blood showed no changes in the membrane fluidity (P > 0.05). In vivo, the membrane fluidity of lymphocytes did not alter significantly during and after infusion of 500ml 10% intralipid at a speed of 100ml per hour into healthy adult (P > 0.05). The level of blood triglyceride was elevated significantly during the infusion (P < 0.01), but decreased rapidly after the infusion. With 500ml per day of infusion (contral group), the surgical patients showed significant decrease in membrane fluidity of lymphocytes after operation (P < 0.01). But there was no significant difference between the study group and control group. The membrane fluidity might be affected by many factors. One of them is membrane lipid. Intralipid mainly contains triglycerides composed of polysaturated fatty acids and lecithin as emulsifier. The result showed that intralipid may neither alter the lipid composition of lymphocytes membrane nor the membrane fluidity. Furthermore, in case of modulation of membrane lipid composition by intralipid occurs, cellular self-regulation may be accomplished by fatty acid synthesis to keep the membrane fluidity stable.