Combined therapy of gemcitabine with interferons on patients with histologically confirmed metastatic renal cell carcinoma is reported. Patients had an unfavourable disease due to documented tumor progression after various interferon-alpha-based immunotherapy (26 weeks on average). The median number of metastatic sites was 6.1 per patient and 78% of the patients exhibited >/= 4 lesions. Nine evaluable patients received at least 6 doses of gemcitabine and 8 doses of interferon-gamma. Overall, therapy resulted in a remission rate of 15% (4 x partial response; 4 x minor response) for single measurable lesions (n=53). Remissions were more often found for lesions, that did not progress at baseline evaluation (n=30; OR: 20%), compared to 8.7% for sites in progression (n=23). However, as a result of therapy, 43.5% of the progressive lesions did not continue to progress. Although only one of nine patients finally overall achieved a minor remission and one patient a stable disease, the median time to tumor progression (6.1 months) and the median survival (13.5 months) was favourable. In conclusion, the combination of gemcitabine and interferon demonstrated cytotoxic and cytostatic effects on metastases of renal cell carcinoma at a tolerable toxicity, thus controlled clinical studies for first line therapy with gemcitabine and interferon are in progress.