We have investigated the serum concentrations of TNF, IL-1 and IL-6 in 49 patients with metastatic renal carcinoma receiving interleukin 2 (IL-2) or a combination of IL-2 and interferon alpha (IFN). Our results demonstrate that IL-2 and/or IFN induce an increase of serum concentrations of IL-1 and TNF in 95% and 75% of the patients respectively. Serum IL-6 levels increase in 44% of the patients. Serum concentrations of IL-1 and TNF remain elevated 48 hours after the end of IL-2 infusion. IL-1 and TNF levels are higher in patients receiving a combination of IL-2 and IFN. TNF and IL-1 levels in serum are significantly higher in responders to IL-2 treatment 48 hours after the end of IL-2 infusion. These two biological criteria enable a subgroup of patients with a very low response rate to IL-2 to be defined. The persistent increase of these cytokines in serum indicates a persistent activation of the immune system lasting after the end of IL-2 treatment which could be involved in the antitumor response.