Respiratory syncytial virus (RSV), originally recovered from a colony of chimpanzees with coryza and designated chimpanzee coryza agent,¹,² and human parainfluenza virus types 1, 2, 3, and 4 have been known primarily as respiratory pathogens in young children. They are now recognized as important pathogens in adults as well. Adults infected with these viruses tend to have more variable and less distinctive clinical findings than children, and the viral cause of the infection is often unsuspected. The consistency of the annual outbreaks of these agents and the frequency of reinfection suggest that they impose a considerable, but ill-defined, disease . . .