INTRODUCTION Besides its common use as a urinary antiseptic, hexamethylenamin is alleged to be beneficial, when administered orally and intravenously, in various infectious diseases. Clinically,1 it has been administered in this way in the treatment of typhoid (Ymaz; Loeper; Ymaz and Ayerza), pneumonia (Loeper; Clarke; Mikhailoff; Loeper and Grosdidier), nephritis (Loeper and Grosdidier; Loeper; de Matta), epidemic encephalitis (Thomas and Rendu), influenza (Loeper and Grosdidier; Michel), serofibrinous pleurisy (Loeper and Grosdidier; Michel), septicemia (Achard), typhus (Glutard), tuberculosis (Loeper and Wagner), prostatitis and epididymitis (Cooke), bronchitis (Mikhailoff; Never), and malaria (Plaschkes and Benkovic). A sound basis for the use of hexamethylenamin in various systemic infections appears to be lacking. However, it is conceivable that certain conditions might exist which would permit hexamethylenamin to exert an antiseptic action. These would be concerned with the liberation of formaldehyd in the blood and tissues. Experimental evidence indicates that hexamethylenamin per se has no antiseptic