Turkey erythrocytes infected with Plasmodium fallax were incubated with C14-phosphatides, -acetate, and -fatty acids in the presence and absence of chloroquine. The C14-labeled lipids were fractionated on silicic acid columns and by paper chromatography, and the radioactivity for each fraction was assayed. The drug depressed uptake of acetate into fatty acids and phospholipids in both malaria-infected and normal erythrocytes. C14-stearic and palmitic acid incorporation into phospholipids of infected erythrocytes was increased by chloroquine while uptake of C14-oleic acid was depressed by the drug. Incorporation of C14-sodium acetate into fatty acids and phospholipids of turkey heart muscle homogenates was inhibited by the drug, and uptake of C14-stearic acid into phospholipids was stimulated by chloroquine.