Clinical, histopathological and DNA cytometric parameters were analyzed before treatment in 57 patients with metastatic renal cell carcinoma (RCC) with regard to their ability to predict objective response to treatment with interferon-alpha (IFN) with or without vinblastine (VB). No pretreatment factor could be identified which was correlated with response. Patients who had at least 30% size reduction of their indicator lesion(s) after 2 months and did not present with new visible metastases had a significantly higher chance to obtain objective response than those in whom this condition was not fulfilled. We suggest that interferon treatment (with or without VB) should be offered for 2 months to all patients with metastatic RCC who are to receive systemic therapy. If at least 30% tumour size reduction is observed at that time, the patient will most probably respond objectively. If the size reduction is less, IFN with or without VB is likely to be ineffective in terms of response achievement.