The nasal and respiratory symptoms observed after oral challenge to aspirin (ASA), tartrazine, and other nonsteroidal anti-inflammatory substances are best described as idiosyncratic reactions. A positive response to oral challenge, defined as a 20% fall in forced expiratory volume in 1 sec (FEV1) from baseline for up to 4 hr, occurred in 44 of 230 patients with ASA, 11 of 277 with tartrazine, 2 of 93 with sodium salicylate, and 2 of 69 with acetaminophen. No one had a positive response to tartrazine, sodium salicylate, or acetaminophen who was not also positive to ASA. The dose of ASA causing a positive response was less than 5 grains in 95% of the patients. Of 50 patients with a suspicious history studied in detail, 96% of those with ASA idiosyncrasy had sinusitis and 71% had nasal polyps. Methacholine challenges and random circulating and sputum eosinophils did not differentiate patients with a negative challenge from those with a positive challenge. However, patients with a positive history and positive challenge had significantly more random nasal eosinophils than those with negative aspirin challenges. The term "aspirin triad" has outlived its usefulness since ASA idiosyncrasy can exist in patients lacking certain components of the triad. ASA idiosyncrasy is unsuspected in many patients and possibly overdiagnosed in others.