In two double-blind trials, volunteers challenged with rhinovirus were treated with aspirin or placebo. Aspirin treatment did not alter the rates of infection or illness but was associated with a moderate reduction in the frequency or severity of some symptoms. The overall benefit in rhinovirus infection was not statistically significant. Aspirin treatment appeared to cause a highly significant increase in the rate of virus shedding in treated subjects. The increase in virus shedding must be considered an adverse event that could influence the course of the disease in the individual and increase the likelihood of the spread of the infection to contacts.