This study was performed with the aim of discovering the characteristics and survival of patients with metastatic renal carcinoma who undergo immunotherapy with an Interleukin 2 based regimen. One hundred and eighty-one patients with metastatic renal carcinoma were referred to our institute from October 1987 until August 1991; 129 were treated with Interleukin 2 with or without Interferon alpha in three successive protocols. Fifty-two patients were not treated with immunotherapy due to the exclusion criteria of the protocols. Sixty-four patients with the same disease who had been referred to our institute before the initiation of this programme (1982, 1987) were also analysed as a control group. The main characteristics of the three different cohorts of patients were analysed and compared with univariate statistical tests; the median survival of the patients was calculated and compared. The referral rate increased from 13 a year to 45 a year while the IL2 trials were being conducted. Patients treated with cytokines have a median survival of 18 months after occurrence of metastases, compared to 6 and 8 months, respectively, in excluded patients and the control group. This parameter is of 15 months when the 181 patients, treated with cytokines or not, are considered. The survival of treated vs excluded patients is significantly different (P < 10(-6); so is the survival of the 181 patients recently included when compared to the historical group (P:10(-5). When the 181 recent patients are compared to the historical control group, a number of differences appear in their characteristics, which prevent us from drawing any conclusion about the role of immunotherapy in the improvement of survival observed. This study clearly evidences the selection of the patients receiving immunotherapy and the modification in referrals of a disease induced by a new available therapy. This emphasises the need for prospective studies in this setting.