A novel device consisting of an infrared-A (= ultrared-A) radiation source equipped with a water filter in the radiation path is described which allows for the therapeutic heating of superficial experimental and human tumors. Preliminary studies with agar phantoms showed that heating in the presence of the water-cuvette avoids intolerable overheating in the very superficial layers. This effect can be further enhanced by surface cooling with room air such that a stratification of the temperature distribution can be achieved. In subsequent experiments, temperature distributions were recorded in the x-, y- and z-axis of superficial rodent tumors. The results obtained confirm those from the phantom experiments, showing that therapeutically relevant temperatures (T > or = 42 degrees C) could be achieved through the tumor mass to a depth of approximately 1.2 cm. Temperature homogeneity is comparable to that seen in superficial tumors undergoing water-bath hyperthermia. This novel technique has proved to be reliable, is well-tolerated, is easy to apply, and is easily accessible to a larger number of potential users for the local heating of superficial malignancies.