Thirty aspirin-sensitive asthmatic patients underwent incremental, oral aspirin challenge until a "positive reaction" (delta FEV1 greater than or equal to 25%) occurred. After this reaction, aspirin was readministered in an attempt to achieve "desensitization." This was defined as the ability of the patient to ingest 650 mg of aspirin without experiencing upper or lower respiratory-tract symptoms or a decrease in lung function. To determine the "refractory period" following aspirin desensitization, patients were rechallenged after various intervals (days) without aspirin until a positive reaction recurred. All 30 aspirin-sensitive asthmatic patients were successfully desensitized to aspirin. Individual patient refractory periods ranged from less than 2 days to greater than 5 days, with most patients gradually returning to sensitivity between 2 to 4 days. Cross-densensitization with indomethacin and other nonsteroidal anti-inflammatory drugs was also demonstrated. These studies show that aspirin desensitization can be safely achieved in aspirin-sensitive asthmatic patients; however, this desensitization will gradually disappear over several days when additional aspirin is withheld.