Sixteen patients with negative routine patch tests were challenged orally in a controlled trial with 2.5 mg nickel, 1 mg cobalt, and 2.5 mg chromium given as salts of the respective metals. All of the patients had symmetrical, vesicular hand dermatitis and in some cases also foot involvement. The dermatitis of two patients flared after challenge with cobalt; in two patients flare occurred following chromate ingestion. Prior to the oral challenge all the patients were patch tested with nickel sulphate, cobalt chloride and potassium dichromate after adhesive tape stripping. Solutions of the same metal salts were used for intradermal testing. The intradermal test sites were read after 20 minutes and 48 hours, the patch tests after 48 h. Skin test reactivity correlated poorly to the results of the oral challenge, possibly due to nonspecific skin test reactivity. It is concluded that oral challenge is a valuable adjunctive diagnostic procedure in patients with pompholyx who have negative routine patch tests.