Several types of reactions to drugs and chemicals may precipitate or perpetuate asthmatic relapse. This review focuses on reactions to aspirin and sulfites. Approximately 40 percent of patients with rhinosinusitis, nasal polyps, and asthma and 5 to 10 percent of all asthmatic patients are sensitive to apirin and aspirin-like nonsteroidal anti-inflammatory drugs at some time in their course. A prudent recommendation to all asthmatics is to substitute acetaminophen for aspirin. When aspirin/aspirin-like drug is essential for treatment of cardiovascular or musculoskeletal disorder, desensitization by cautious oral challenges with graded doses of aspirin can be accomplished. Treatment of the respiratory disorder per se by desensitization followed by daily therapeutic aspirin remains investigational. Sulfur dioxide and sulfites, commonly used as sanitizers and preservatives of foods and pharmaceuticals, may precipitate acute asthma in 5 percent or more of asthmatic patients. When the history suggests sulfite sensitivity, challenges can be used to confirm sensitivity and the patient counseled in avoidance of these chemicals.