Summary 1. The clinical, pathologic, mycologic and serologic findings in a case of verrucous dermatitis (chromoblastomycosis) occurring in a native of the United States are described, this being the first case due to Hormodendrum pedrosoi to be reported in the United States. 2. Single spore isolation from cultures of the causative organism revealed sporulation characteristic of three different genera of fungi. 3. Specific complement-fixing antibodies to the fungus were found in the serum of this patient, and a cross-antigenic relationship was demonstrated between strains of Phialophora and Hormodendrum isolated from various cases of the disease. 4. Iontophoresis treatment with coppper sulphate was followed by marked clinical improvement in the skin lesions and by a great reduction in the number of fungi in the skin.