The effectiveness of local hyperthermia was investigated in 56 patients with locally advanced carcinoma of the rectum (T4N0M0). All received combined heat and radiation therapy as a pre-operative treatment. The control group consisted of 59 patients with the same stage of disease as those who were only irradiated. Both groups of patients underwent the same surgical procedure. The total tumour dose of ionizing radiation was 40 Gy in 10 fractions, three times a week. The tumour was heated four or five times to a maximum of 42-43 degrees C by electromagnetic waves with a frequency of 905 MHz before irradiation. Each heating session lasted 60 min. Patients were selected on the principle of randomization: 16.1% of patients (n = 9; n: actual number of patients) showed complete response and 53.6% (n = 30) showed significant regression of the primary tumour compared with 1.7% (n = 1) and 33.9% (n = 20) in the control group, respectively. The differences were significant (p less than 0.05). It was found that thermoradiotherapy allowed the 5-year survival rate of patients to increase up to 35.6% (n = 12) compared with 6.6% (n = 7) in the control group (p less than 0.05).