The authors determined the safety and efficacy of recombinant high-dose interleukin-2 administration in patients with brain metastases. This retrospective review included 1,069 patients with metastatic melanoma or renal cell carcinoma who received high-dose interleukin-2 alone or in combination with other immunotherapy or chemotherapy from July 1985-July 2000. All patients were evaluated for both toxicity and response. Only the first exposure to interleukin-2 was considered. Parameters evaluated among the groups included toxicity profiles, reasons for stopping treatment, number of interleukin-2 doses per cycle, and response to therapy. Three patient groups were compared. Group I (n = 27) comprised patients with previously treated brain metastases (surgery or radiation), group 2 (n = 37) comprised patients with untreated brain metastases, and group 3 (n = 1,005) comprised patients without brain metastases. For most comparisons between patients with brain metastases and those without, no significant differences were noted in toxicity profiles or reasons for stopping interleukin-2 therapy. Patients with previously treated brain metastases received fewer interleukin-2 doses per cycle (median, 6.5) than patients with previously untreated brain metastases (median, 7.5) or patients without brain metastases (median, 7.5). Patients with previously treated brain metastases demonstrated an 18.5% overall clinical response to interleukin-2 treatment. However, patients with evaluable (previously untreated) brain metastases had an overall 5.6% response rate, which was less than the 19.8% response rate of patients without brain metastases. Two of thirty-six patients with evaluable brain metastases demonstrated objective regression of intracranial and extracranial disease after receiving interleukin-2. Carefully selected patients with brain metastases can safely receive high-dose interleukin-2, and some can experience a response to treatment at intracranial and extracranial disease sites.