The objective of the present study was to validate the use of intralesional injection of interleukin-2 (IL-2) in patients with skin and soft-tissue melanoma metastases. A total of 24 patients with AJCC stage III or IV melanoma and single or multiple skin and soft-tissue metastases were included. Interleukin-2 injections were administered intralesionally into the total number of cutaneous and soft-tissue metastases accessible from the skin, 2-3 times weekly, over 1-57 weeks. Single doses varied from 0.6 to 6 x 10(6) IU, depending on lesion size. The clinical response was monitored by sonography and confirmed by histopathology; response evaluation was confined to the intralesionally treated tumours. Complete response (CR) of the treated metastases was achieved in 15 patients (62.5%), the longest remission lasting 38 months to date. In five patients, partial response (PR) was achieved (21%) and in another three patients, progressive disease was observed (one patient not assessable). A total of 245 metastases were treated with CR in 209 (85%), and PR in 21 (6%). The therapy was generally well tolerated; the observed adverse events were mainly of grade 1-2 severity. Immunohistochemical studies showed the tumour cells undergoing apoptosis and revealed a mixed character of the inflammatory infiltrate. The unusual high CR rate in metastatic melanoma of 62.5% and the limited toxicity suggest that treatment of skin and soft-tissue melanoma metastases with intralesional injection of IL-2 may be a safe and effective alternative to conventional therapies. The optimal dosage and duration of this therapy still remain to be defined in larger prospective multicentre trials.