Twenty previously treated patients with advanced bone sarcomas received thrice weekly im 50 X 10(6) IU/m2 doses of human alfa-interferon (interferon alfa-2a, recombinant; Roche). Seventeen patients had metastatic osteosarcomas and one each had fibrosarcoma, mesenchymal chondrosarcoma, and malignant fibrous histiocytoma. Two patients with osteosarcoma and the one with malignant fibrous histiocytoma experienced objective partial tumor regression for 1, 3, and 2 months, respectively. Fever, anorexia, myalgia, fatigue, lethargy, and moderate myelosuppression were observed commonly, and some patients developed mild nausea, vomiting, and diarrhea. No patient withdrew because of toxicity and no dose reductions were necessary except adjustments for changes in body surface area secondary to weight loss.