Allergic-like reactions to chemical components of foods and medicines may be common. The prevalence of idiosyncratic reactions to aspirin, salicylate, metabisulfite and tartrazine is not known. We used a tertiary referral clinic population to estimate safe exposure doses for epidemiological studies. A 15% decrease in the amount of air expired in one second was defined a positive response. The median effective molar doses of the agents were remarkably similar: metabisulfite 0.19 mM, 34.4 mg [95% confidence interval (CI) 0.14, 0.27 mM]; tartrazine 0.10 M, 55.0 mg (95% CI 0.05, 0.21 mM); aspirin 0.09 mM, 16.5 mg (95% CI 0.04, 0.19 mM); and salicylate 0.11 mM, 15.3 mg (95% CI 0.05, 0.27 mM). Doses to which the most sensitive (5%) and practically all (95%) susceptible persons might respectively respond are: metabisulfite 4.6 mg, 255.8 mg; tartrazine 3.4 mg, 885.6 mg; aspirin 0.8 mg, 332.3 mg; and salicylate 2.6 mg, 89.9 mg. Doses within these ranges can be used in epidemiological studies.