The acantholytic action of cantharidin was tested on freshly isolated human skin and on the skin of live guinea pigs. Acantholysis could be inhibited by pretreating the skin with subepidermal vesicants or by incubating isolated skin in a nitrogen atmosphere. The results and those of varying temperature and oxygen tension led to the conclusion that cantharidin requires an intact and active energy supply system for its acantholytic action. Some differences between the vesicant action of cantharidin and subepidermal vesicants are pointed out. The possible relationship between the mechanism of chemical blister induction and the development of spontaneous blisters in certain dermatoses is discussed.