Twenty-six normal volunteers were exposed to rhinovirus or influenza B virus. Measurement of nasal mucociliary clearance, ciliary beat frequency, percent of epithelium ciliated, ciliary ultrastructure and nasal transmucosal potential difference were made before exposure, during viral incubation and at the time of expected overt infection. Ten volunteers failed to become infected, six were subclinically infected and nine were infected with symptoms. There were no significant differences between the results in volunteer groups during the incubation period or between uninfected and subclinical groups at the time of expected symptoms. Six of nine symptomatic infected volunteers had prolonged nasal clearance, and six of the seven biopsied had less than 50% of their epithelium ciliated. However, there was no significant reduction in ciliary beat frequency nor increase in ultrastructural ciliary abnormalities within this group of symptomatic volunteers. Of the two symptomatic infected (influenza B) volunteers tested, both showed significantly reduced transmucosal potential difference.