Recently, we applied inhalation of recombinant interferon (IFN)-gamma, to 4 patients with pulmonary metastatic tumor (3 with renal cell carcinoma and 1 with renal pelvic tumor). Of the patients with renal cell carcinoma 2 had received previous nephrectomy, 1 patient had received embolization alone, 1 subcutaneous IFN-gamma in 1, and 1 systematic chemotherapy. All 4 patients inhaled 1 x 10(6) JR U-2 x 10(6) JR U recombinant IFN-gamma 3 times per day. Additionally, all metastatic renal cell carcinomas received subcutaneous injection of IFN-gamma. One patient with renal cell carcinoma achieved a complete response after inhalation therapy and 2 patients did not respond (NC: 1, PD: 1). A case of metastatic renal pelvic tumor did not respond. Immunohistochemical staining with antibody to Ber-MAC3 (stimulated macrophage) of this case revealed positive cells within the transitional cell carcinoma. According to these results, inhalation of IFN-gamma appears to be applicable as one treatment for pulmonary metastatic tumor of renal cell carcinoma.