To examine whether levels of inflammatory cytokines and eosinophil cationic protein (ECP) in the sputum reflect the severity of bronchial asthma, we measured their levels in the sputum of symptomatic and asymptomatic asthmatics. Interleukin (IL)-1 beta, IL-5, IL-6, IL-8, RANTES, tumor necrosis factor-alpha and ECP concentrations in the sputum of symptomatic patients were significantly higher than in asymptomatic subjects. These findings suggest that these inflammatory cytokines are involved in the exacerbation of asthma.