Pompholyx (Dyshidrosis) is a disease of unknown etiology presenting as symmetrical, vesicular hand and foot dermatitis. To clarify the pathogenetic role of sweat and metal allergy, twenty five patients with pompholyx were examined with respect to their perspiration volume using equipment that continuously recorded the local perspiration volume. Patients were also examined for metal allergy by patch testing and oral challenge tests. The perspiration volumes were measured using recently developed equipment for continuous recording of local perspiration volume (Kenz-Perspiro oss-100). The perspiration volume of pompholyx patients was found to be 2.5 times higher than that of age-matched normal controls. Twenty percent of the patients showed sensitivity to chromate, 16% to cobalt, and 28% to nickel on patch testing. Six patients with positive results were challenged orally in a controlled trial with 2.5 mg nickel, 1 mg cobalt, or 2.5 mg chromium. Four of them (67%) showed vesicular reactions on their hands with challenge testing. These results indicated a sensitivity to metal compounds which, in combination with local hyperhidrosis, may contribute to the development of vesicular lesions in pompholyx.