Interleukin-2 (IL-2) and interferon alfa-2a (IFNalpha2a) have some antitumor activity in metastatic renal cell carcinoma either alone or in combination. To determine whether either of these cytokines might be efficient after failure of the other, we analyzed a series of patients treated with either IL-2 or IFNalpha2a as second-line treatment after failure of the other cytokine.