The "baboon sydrome" is the term used to denote a characteristic distribution pattern of systemic allergic contact dermatitis. Such skin manifestation is described as mercury exanthem in Japan. Until now, mercury, ampicillin, nickel is reported to produce this condition. We report herein 3 cases of the baboon syndrome. Among 3 cases, 2 cases were associated with mercury, but in the other we could not demonstrate the allergen.