(1) A significant reduction in platelet adhesiveness averaging 15% can be measured during infusion of 500 ml of 20 percent Intralipid® using the Hellem method. The initial degree of adhesiveness is reestablished to a large extent 4 h after termination of the infusion. (2) The platelet count does not change significantly during Intraplipid® infusion. (3) The serum lipids reach maximum concentration at the end of the infusion period. These concentrations drop rapidly after termination of infusion, they are almost back to the starting point after 4 h. (4) Control infusion using a physiological sodium chloride solution or a 5-percent glucose solution produces consistent fluctuations in the lipids except an expected decrease of FFA during glucose infusion. There is no significant change in adhesiveness. (5) In contradistinction to tests carried out in vivo, the in vitro tests show a significant increase in platelet adhesiveness after the addition of Intralipid® to whole blood. (6) The results together with the clinical experience indicate that the parenteral administration of the fat emulsion Intralipid® is a safe procedure.