THE BLOOD of patients with acute disseminated lupus erythematosus has been found to contain a factor which can be detected by adding the whole plasma of these patients to preparations of human or dog bone marrow. This presentation is concerned with the detection of the "L. E. factor," with its disappearance during complete remissions of the disease and with its identification or association with the gamma globulin fraction of the plasma. Study of the bone marrow was introduced as an investigative field in acute disseminated lupus erythematosus by work originally done at the special hematology laboratory of the Mayo Clinic. Richmond1 detected a phenomenon of phagocytosis in the bone marrow of a man who was extremely ill with an undetermined disease. Characteristic of this phenomenon was the cell, which she called the "tart cell." This cell is a polymorphonuclear leukocyte which contains a small inclusion. Hargraves