Experiments on rat rhabdomyosarcomas R1H were performed to evaluate the therapeutic potential of a simultaneous radiation-hyperthermia treatment of superficially growing tumours. Tumours were heated locally with infrared-A radiation and irradiated in the middle of the heating period. After a treatment with 32 Gy in 8 fractions combined with 8 heat fractions of 43 degrees C, 1hr, during 4 weeks, tumours showed an enhanced regression and growth delay in comparison to radiation alone. A thermal enhancement ratio (TER) of 1.4 was determined. Acute skin reactions were of minor importance. In conclusion, a simultaneous treatment of superficial tumours with infrared-A-hyperthermia and radiation at a therapy unit is relatively easy to perform and enhances considerably the therapeutic efficacy of a radiation treatment.