To the Editor.— Early fears that live oral poliovirus vaccine, monovalent type III might produce disease in the young adult group have not been borne out in the military population. The US Army has administered type III live oral poliovirus vaccine to more than 3.5 million young adults since 1963. The vaccine initially used was monovalent, given four to six weeks after type I monovalent vaccine in either one of two schedules. Since 1966 trivalent oral poliovirus vaccine has been given either as two doses eight or more weeks apart or as two doses four weeks apart followed by a third dose eight or more weeks later. Since June 1964, no cases of paralytic polio have been reported in US Army personnel. During this same period several hundred thousand adult military dependents also received the vaccine. No vaccine-associated cases have been reported to us from among this group. Therefore, it