Behnisch and his co-workers1 at the laboratories of Farbenfabriken Bayer at the Elberfeld Works, Germany, have developed, in cooperation with Domagk, a group of chemical substances, thiosemicarbazones, which possess chemotherapeutic effect against tuberculosis. The activity of these products, according to these investigators, is not dependent on the sulfonamide or sulfone groups, nor on the thiazole or thiodiazole rings, but on an open chainlike arrangement of the nitrogen and sulfur atoms, such as is present in the thiosemicarbazones when suitably substituted. The most active of these substances is 4-aminoacetylbenzaldehyde thiosemicarbazone, designated as conteben or TbI/698. Domagk2 states that this substance has an effect on the tubercle bacillus in vitro and in vivo. He demonstrated in experimental tuberculosis in guinea pigs that the effect is much like that of para-amino-salicylic acid. Although the mode of action of the drug has not been established, Domagk believes that it exerts a direct