The rate at which interferon is cleared from the nose after local administration was measured in volunteers both before and after challenge with virulent strains of human rhinovirus. Interferon was not cleared more rapidly after virus challenge, and there was no relationship between the amount of nasal secretion produced after challenge, and the rate of interferon clearance. These findings suggest that an inverse relationship between the quantity of a locally applied antirhinovirus drug which is recovered in nasal wash, and clinical and laboratory evidence of rhinovirus infection may be taken as evidence for a beneficial effect of the drug.