Pyrithyldione (presidon,® 3,3-diethyl-2,4-dioxotetrahydropyridine) is a mild hypnotic and sedative, not a barbiturate derivative, which is now being widely employed. Several reports which recommend its use as a sedative indicate a tendency of the drug to depress the granulocyte count. Koppanyi and others in 1940 noted that in rabbits receiving pyrithyldione by mouth13 animals exhibited a decrease in the percentage of circulating polymorphonuclear leukocytes from 34 to 11, 24 to 12, and 19 to 9 per cent, respectively. However, the animals survived after the drug was discontinued. An even more significant observation on human subjects was recorded by Polatin and Horwitz in 1947.2In a series of 10 patients whose white blood cell counts were carefully followed daily during three weeks' administration of the drug (600 mg. daily), they noted that 1 patient's total white blood cell count dropped from 8,700 to 3,850 with no change in the