The potential involvement of interleukin-1 (IL-1) in the pathogenesis of experimental rhinovirus colds was examined. Nasal lavages were recovered before and for 5 days after rhinovirus infection from 44 subjects, 22 of whom were randomized to receive prophylaxis with glucocorticoids, while the rest received placebo. Immunoreactive IL-1β was significantly increased in subjects who were infected and symptomatic compared with noninfected volunteers or subjects who were infected but asymptomatic. Concentrations of immunoreactive IL-1β correlated with levels of kinins and albumin in lavagefluids, Studies of IL-1 bioactivity established that most activity in lavages from infected subjects was IL-1β. Glucocorticoid prophylaxis did not inhibit IL-1 production, nor did it significantly affect the symptomatic response to infection or, in a subset of patients, neutrophil infiltration. These data are consistent with the hypothesis that IL-1 could contribute to the pathogenesis of rhinovirus infections.