Optically isolating each of the sensory elements or ommatidia of the eye of the fruitfly, Drosophila mdanogaster, are groups of pigment cells. To these the eye owes its color. In the wild-type eye the cells contain granules which range in color from yellow to red or purplish red.The main body of the eye pigments can be extracted with water. The solutions exhibit characteristic color changes with pH and with oxidizing and reducing agents (cf. Schultz, 1935; Laki, 1935,36). Two groups of pigments appear to be present in the wild-type eye, designated as the red and the brown components (Mainx, 1938). The mutant scarlet, vermilion, and cinnabar eyes apparently contain only members of the red component, brown eyes only the brown component (Wright, 1932;Mainx, 1938). According to Mainx only the red component dissolves readily in water. The brown component is much more difficultly soluble; it is irreversibly decolorized and simultaneously dissolved by alkaline solutions.Some evidence exists that the red component is multiple in nature (Ephrussi, 1945), and that the red component pigments are different in sepia and wildtype eyes (Mainx, 1938). Pigments of both groups appear to contain a high proportion of nitrogen. Lederer (1940) reported 19 per cent N in a red pigment from wild-type eyes, Becket (1942) 6.79 to 17.2 per cent N in so called "ommatine" pigments of insects, which he believed include the brown component of the Drosophila eye. The latter appears to be derived from tryptophane through the intermediate formation of a-oxytryptophane and kynurenin (Beadle and Tatum, 1941;Butenandt, Weidel, and Becker, 1940 a, b;Kikkawa, 1941).The present experiments are a contribution toward the fractionation and characterization of the eye pigments of wild-type and mutant Drosophilas.They were performed in 1941-42, and were interrupted by the departure of one of us for military service. OBSERVATIONSWhole heads of flies (500 to 1500, 1 to 4 days after emergence) were extracted with distilled water after grinding in a mortar. As a control for the possible presence of pigment in head tissues other than the eye, similar numbers of heads of whiteeyed flies were extracted. They yielded negligible amounts of pigment.