This prospective study was carried out to explore cytokine-related immune alterations in 69 renal cell carcinoma patients (RCC) and to look for changes which might potentially serve as a reliable predictors of response to cytokine-based therapy. Interleukin-2 (IL-2), its soluble receptor (sIL-2R) and tumor necrosis factor (TNF-alpha) levels produced in vitro by PHA activated and intact mononuclear cells (PBMC) were determined. Concentrations of IL-2, IL-4, IL-6, sIL-2R, TNF-alpha and CRP were measured in sera. Cytokine level was evaluated by enzyme-linked immunoadsorbent assay (ELISA) and CRP was determined by means of turbidimetric method. All measurements were performed in patients without any prior treatment. PHA activated PBMC of RCC patients were significantly defective in producing IL-2 and TNF-alpha comparing to controls (p < 0.03 and p < 0.001). The difference of sIL-2R was noted in metastatic stage only (p < 0.03). Unstimulated PBMC manifested decrease in IL-2 (p < 0.03) and increased level of TNF-alpha in advanced disease (p < 0.02). This impairment reflected tumor size and differentiation stage. Serum concentrations of IL-2, sIL-2R and TNF-alpha were within normal range. However, in relation to the clinical stage, significantly increased serum IL-2 was noted in combined Stage I and II as compared to controls (p = 0.012). IL-6 and CRP showed markedly elevated levels with a significancy which allowed to distinguish samples from metastatic patients. In conclusion careful comparisons of these data with clinical course of cytokine treated patients will disclose which of those tests may possess predictive power in the individual patients who are likely to respond to cytokine-based treatment.