Viruses are recognized to be the major cause of respiratory infections. Clinical and experimental evidence also supports an important role for viruses in the pathogenesis of lower airway disease and asthma exacerbation. In prospective epidemiological studies, 80% of asthma exacerbations in school-aged children and half of all asthma exacerbations in adults have been associated with viral upper respiratory infections. Human rhinovirus (HRV) has been implicated as the principal virus associated with asthma exacerbation. In our studies on respiratory viruses, we have observed two clinical patterns of presentation. The viruses can either be a precipitating factor of respiratory illness characterized by a typical clinical onset, or can induce an atypical clinical onset such as haemoptysis, pleuritis, spontaneous pneumothorax and asthmatic syndrome. Thus the observed clinicoradiological and functional features during atypical viral respiratory infection may be correlated to the long-term biological effects induced by previous and concurrent infections.