The method of preparing a colloidal solution of cholesterol and lecithin for intravenous injection is described. Cholesterol injected intravenously in cats is highly toxic; however, the toxicity can be modified somewhat by the addition of lecithin to the solution. Tables are presented showing that after injection the cholesterol content of the blood is diminished while that of the liver is moderately increased and of the lungs, enormously so. Anesthesia, paralysis, reduction of heart rate and great acceleration of respiration rate are short-lived phenomena immediately after injection. Vagotomy reduced the cardiac and respiratory effects. Moderate to severe acidosis developed. Electrocardiograms showed transient inversion of T and prolongation of P-R interval, sometimes actual heart block and ectopic complexes. Blood surface tension was increased moderately; red cell fragility was unchanged. No change in blood sugar was demonstrated.