Medical Corps, United States Army Case 1.— A white man aged 46 with moderately advanced pulmonary tuberculosis, was admitted to Fitzsimons General Hospital in January 1947. On April 1 the patient was started on 2 Gm. of streptomycin daily, intramuscularly in five equally divided doses. There was no history of blood disorder or any evidence of such on periodic examinations until June 19, at which time the erythrocyte count was 3,100,000, the leukocyte count was 3,500, neutrophils 54 per cent and lymphocytes 46 per cent. Streptomycin was discontinued on that date. On June 29 the leukocyte count was 2,000 with 91 per cent lymphocytes. The platelets were markedly decreased. On that date, the usual vigorous measures were begun to combat aplastic anemia. In spite of this the blood picture continued to deteriorate until July 7, when the erythrocyte count was 2,800,000. The leukocytes measured 800, of which 2 per cent