An increasing number of reports have indicated that palladium chloride (PdCI2) is a sensitizer in humans. The guinea pig maximization test method has shown that PdCI2 is a potent sensitizer. The simultaneous reactivity to PdCI2 and nickel sulfate in some patients does not seem due to contamination of the salts used for testing. The question of cross-reactivity can be elucidated by using this sensitive animal model.