While ingesting selected foods and drinks in restaurants, four asthmatic patients reported the sudden onset of severe wheezing and associated anaphylactoid symptoms and signs. Single-blind placebo and potassium metabisulfite (K2S2O5) oral challenges documented asthmatic responses 15 to 30 min after ingestion of K2S2O5. Laboratory investigations failed to demonstrate specific reaginic antibody recognition of K2S2O5 in these patients. Furthermore, their peripheral basophils did not release histamine during in vitro challenges with K2S2O5. It seems likely that additional asthmatic subjects have such sensitivities but are currently assumed to have "food allergies." Such individuals can be suspected of having this sensitivity by history, and oral K2S2O5 challenges can identify asthmatics who are sensitive.