To determine the incidence of wheezing in adult asthmatics with rhinovirus infection, we exposed 21 asthmatic volunteers to 1 of 2 rhinovirus serotypes. Symptoms, spirometry, and histamine inhalation challenge were assessed prior to, daily during, and 3 wk after the rhinovirus infection. Four volunteers had fiberoptic bronchoscopy performed on the fourth study day. Nineteen volunteers became infected with rhinovirus; 17 of 19 had typical coryzal symptoms. Volunteers did not have significant changes in spirometry or histamine sensitivity during rhinovirus infection when taken as a group or when categorized by severity of asthma or severity of the clinical illness. A subgroup of 4 volunteers was identified that had a 10% or greater decrease in FEV1 and a parallel increase in histamine sensitivity during rhinovirus infection; these 4 volunteers were not otherwise distinguishable from the group as a whole. Rhinovirus was recovered from bronchoscopy specimens of 1 of the 4 infected volunteers bronchoscoped. Thus, exacerbations of wheezing occurred in the minority of experimental rhinovirus infections in adult asthmatics, suggesting that other viral pathogens may play a more important role in precipitating asthma attacks.