Tricaprin increase the rate of spreading of macrophages on glass. The treated cells showed increased pinocytosis and are avidly phagocytic. Cholesterol oleate delays the onset of phagocytosis which however proceeds efficiently once it has begun. Ethyl palmitate induces abnormal movement and the formation of unusual club shaped pseudopodia; ethyl palmitate prevents the ingestion of antibody coated erythrocytes and it is postulated that this substance interferes with the syntheses of IgG receptors.