Bowen's disease is a form of squamous cell carcinoma in situ, in which local hyperthermia may be efficacious. We studied 8 patients with Bowen's disease to ascertain whether hyperthermia can be effective against it. As a heat source, disposable chemical pocket warmers were applied daily with pressure directly to the lesion site while the patient was awake, and the clinical course was observed for 4 to 5 months. The lesion was then excised and examined to determine the histopathologic effects. The results showed efficacy in 6 cases, in which the nodular and invasive lesions and the erythematous patches abated; then the lesions disappeared, leaving deposits of pigment (complete remission). In one case, the signs improved by at least 50% (partial remission); in the other case, there was only slight palliation (no response). As for the posttreatment histopathologic effects, tumor cells were eliminated in 3 cases, isolated tumor cells were seen in 3 cases, and there was no change in 2. Although the treatment did not yield perfect results, it represents a major improvement of hyperthermic therapy and is one effective method of treating Bowen's disease.