Patients with a sore or burning mouth associated with clinically normal oral mucosa present a difficult diagnostic challenge. The objective of this study was to assess the value of patch testing in patients with burning mouth syndrome. We retrospectively reviewed the results of patch testing to an oral series in patients with burning mouth syndrome seen at Mayo Clinic, Rochester, Minnesota, between January 2000 and April 2006. Of 195 consecutive patients with a burning or sore mouth, 75 had patch testing to an oral series, and 28 of these patients (37.3%) had allergic patch test reactions. The most common allergens were nickel sulfate hexahydrate 2.5%, balsam of Peru, and gold sodium thiosulfate 0.5%. On follow-up, 15 patients reported improvement, 4 removed or avoided the offending dental metal, and 6 avoided the dietary allergen. Thirteen patients did not improve; 6 avoided identified allergens, but without improvement; 1 removed dental metals without symptom change; and 5 avoided test-positive dietary allergens but without improvement. The remaining 7 nonresponders had nonrelevant patch test results or did not avoid allergens. Patch testing can identify patients who may be allergic to dental metals or dietary additives and who may benefit from removal or avoidance of these.