A mutant of Drosophila melanogaster possesses pigmented, stationary cells in the body cavity of the pupal and adult stages. The pigment is present as numerous red granules in the cytoplasm. By a number of criteria, the pigmented cells are a type of fat cell. The evidence suggests that the pigment is related to, or identical with, the brown component of the eye pigment and that it develops in the fat cells autonomously.