To diagnose Aspirin-induced asthma (AIA) safely and steadily, we performed an inhalation challenge test with a solution of Aspirin DL-lysine (VenopyrinⓇ) in 35 bronchial asthmatics. This test was positive in 15 asthmatics including 12 symptomatic AIA cases. Three of the 23 symptomatic non-AIA patients, showed a positive reaction by aspirin inhalation. All 4 patients, who had a positive result in the aspirin oral challenge test, also showed a positive reaction in the aspirin inhalation challenge test. However, during the inhalation experiment there was no evidence of large attacks provoked by the aspirin oral challenge test, indicating the safety of the inhalation challange test. Thses findings suggest that the test may be important for prevention of progression of intractable asthma by detection of latent AIA patints.