The therapeutic effect of intratumoural application of Interleukin-2 (IL-2) was studied in patients with stage III-IV nasopharyngeal carcinoma (NPC) that received radiotherapy. Patients with stage III-IV NPC receiving a standard treatment of 7,000 cGy external beam irradiation have a mean disease-free survival of about 1.5 years. In this paper, we describe ten of these patients who were treated with additional peritumoural and intratumoural injections with 3 x 10(4) U IL-2 on 5 days in weeks 2, 4, and 6 of the 7-weeks' irradiation period. This combined treatment group was compared with a historical group of patients treated with standard irradiation alone. Local IL-2 therapy showed a marked clinical and statistical significant improvement of disease-free survival. After 5 years, 63% of the IL-2 treated patients were disease-free versus 8% of the control patients. These results suggest that the therapeutic results of radiotherapy can be significantly improved by combining it with local IL-2 treatment. To our knowledge, this is the first clinical report showing that local IL-2 therapy is effective against an infiltrative and locally metastasizing tumour in human patients.