Abstract
The role of viruses and M. pneumoniae in episodes of acute respiratory illness in childhood has been studied in a London general practice. The total isolation rate was 31-7 per cent, but the rate varied from 32-6 per cent in upper respiratory infections to 64-0 per cent in pneumonia. The clinical features associated with infection were influenced not only by the type of agent but also by age and other host factors in infected children. Rhinoviruses were more commonly isolated than any other agent and were frequently associated with wheezy bronchitis.