Histologic and electron microscopic studies of Solcoderm-treated normal skin and human lesions were performed to help elucidate the mode of action of this new agent. Its fixative properties were readily demonstrated and generally proved to be adequate for histological diagnosis from the post-treatment scab. The degree of preservation of fine intra-cellular structures was particularly remarkable, since similar treatment with equivalent strengths of nitric acid alone destroys these substructures. Dermal lipids and collagen were found to be natural barriers against the penetration of Solcoderm applied to the skin surface. Mild mechanical disruption and the disturbed cellular continuity of pathologic tissue allows the solution to penetrate treated lesions more freely and enhances the likelihood of their complete destruction when an appropriate quantity of solution is properly delivered by an experienced therapist.