Cantharides blisters were produced on the skin of allergic human subjects. After removing the stratum corneum over the blisters, the denuded areas were covered with saline, and the release of histamine and protein into the saline was determined before and after production of local allergic reactions by injection of antigen. Both the histamine and the protein content of the saline rose sharply within a few minutes after injection of the allergen and fell to the original level within 60 minutes. An increase in exudation of fluid and the appearance of a substance similar to the “slow reacting substance” were also observed.