C. D. (Case A40,933), a five-year-old white boy, was first admitted to the hospital in February 1940, with a history of pain in the joints and recurrent fever of seven months' duration. During this time he had been treated for acute rheumatic fever, without improvement. Onset of the pain had been in the right knee and right lower leg, and the knee joint had been moderately swollen and tender. Subsequently, similar episodes occurred involving the other knee and both ankles and elbows. Symptoms subsided after several weeks but recurred in spite of bed rest and salicylates. It was noted that each episode was associated with tenderness along the shafts of the adjacent long bones. Past history and family history were not contributory. Physical examination on admission showed a pale, under-nourished, under-developed boy with slightly swollen tender knees and elbows. Temperature was 99.8°, pulse 100, and respirations 20. The positive findings were marked pallor of the mucous membranes, a blowing systolic murmur at the cardiac apex, and limitation of motion of the elbows and knees due to pain. There was exquisite tenderness along the shaft of each tibia from the knee to the ankle. There were no enlarged lymph nodes and no abdominal organs or masses could be felt. Laboratory examinations showed a hemoglobin of 50 per cent (S) with 2,800,000 red blood cells. The white blood cells numbered 2,000, of which 68 per cent were adult lymphocytes. The Wassermann reaction was negative and blood chemistry and urinalysis were normal. A biopsy of the sternal marrow was performed. Roentgen examination of the skeleton showed numerous punched-out areas of rarefaction in the skull, pelvis, and the diaphyses of the femora and tibiae. All the long bones showed a striking, smooth, regular periosteal proliferation extending along the shafts. (Figs. 1, 2, 3.) During the next two months the patient remained chronically ill, and enlargement of the liver, spleen, and lymph nodes appeared. Dr. Belk: Before proceeding to a discussion of the differential diagnosis, I think we should be told about therapy, inasmuch as this patient's response to therapy has diagnostic significance. Dr. Taylor: This little boy was given supportive therapy, including iron and vitamins and numerous small transfusions during the eight months before his death. Roentgen radiation in divided doses totalling 300 r, given with an intermediate-voltage unit, proved specific in relieving bone and joint pain. In addition, small doses (10 r) of whole body irradiation at 70 cm. at weekly intervals seemed to maintain the child in fairly good health during most of the summer before his death. With the coming of October, the patient began to lose ground steadily in spite of treatment. Subcutaneous ecchymoses and a persistent neutropenia developed. The week before death, the white count was 300 with absence of polymorphonuclears. This agranulocytosis was associated with generalized furunculosis.