Acute respiratory and diarrheal diseases cannot be expected to be effectively controlled by vaccines for a variety of reasons but largely because of the great multiplicity of causative agents. Measles could be eradicated by appropriate strategies. Paralytic poliomyelitis caused by polioviruses can be controlled by oral poliovirus vaccine in both developed and undeveloped countries but by different strategies. Vaccines cannot be expected to have a beneficial effect on recurrent genital, ocular, and facial herpes. Since naturally acquired immunity does not prevent subsequent fetal intrauterine infection with cytomegalovirus, it is still necessary to establish whether it can nevertheless prevent congenital defects. Prospective hepatitis B vaccines cannot be expected to be useful in the general population. There is reason to believe that both varicella and herpes zoster could be prevented by widespread use of the Japanese attenuated vaccine.