A Ewing sarcoma grown in immunosuppressed mice was eradicated with a single lethal dose of dimethylmyleran (DMM) followed by autologous or syngeneic bone marrow. Sarcomas treated 2 weeks after grafting in a phase of rapid proliferation disappeared and large sarcomas treated after 6 or 10 weeks were reduced to necrotic tissue. A human osteosarcoma also regressed distinctly after this therapy while a human colon carcinoma responded poorly. Sub-lethal DMM treatment induced complete remissions in only 62% of the mice. Tumours which display sensitivity in this model may be treated clinically with lethal doses of DMM and autologous marrow transplantations.