A fraction was obtained from Plasmodium berghei which induced hemolysis of the erythrocytes of mice and hamsters. This fraction, called lytic factor (LF), was found to be composed of a large amount of lipid material. An examination of the lipids showed the major lipids to be monoglycerides, diglycerides, triglycerides, fatty acids, long-chain alcohol, sterol, sterol ester, sterol glycoside, and two cerebrosides. The most abundant component found in the LF was sterol ester, followed in order by cerebrosides, sterol, and sterol glycoside. Lytic activity was found to be lost when samples were boiled for 5 min. An examination of the lipid composition of LF before and after boiling showed changes which may be useful in studies on the mechanism of activity of this factor. The fatty acid composition of the total lipid fraction of LF was examined by gas-liquid chromatography. The major fractions were 18:1 and 16:0 in unheated LF and 16:0 in the heated LF.