Warts are viral tumors of the epidermis. They may be destroyed by a great variety of physical and chemical means; while none is perfect, most are useful. Because of the special ability of cantharidin to disorganize epidermal cells, we decided to explore its use as a chemotherapeutic agent in warts. Materials and Methods Cantharides is dried, powdered blister beetle. Cantharidin is its purified active ingredient.* Its primary cutaneous effect is the separation (acantholysis) and death of epidermal cells.1 For topical treatment, cantharidin is prepared as a 0.7% solution in equal parts of acetone and flexible collodion U. S. P. The cantharidin is first dissolved in acetone. The solution should be kept in a tightly stoppered bottle. The kind which has a glass rod fixed to the cap is convenient for applying the solution. Some degree of evaporation with usage is inevitable but ordinarily may be disregarded, since