Arachidonic acid metabolites are measured in primary osteogenic sarcomas, benign neoplasms, and tumor-like bone lesions. In typical osteogenic sarcomas, the contents of E and F2~ prostaglandins are significantly higher than in benign bone tumors or tumor-like bone lesions. Neoadjuvant chemotherapy has different effects on the levels of prostaglandins E and F2,, thromboxane B v and prostaglandin F~ in osteogenic sarcomas, its effectiveness depending on the mechanism of drug action and individual sensitivity of tumor cells to this drug. A negative correlation is established between the content of prostaglandins E in osteogenic sarcoma and the degree of therapeutic pathomorphosis of the tumor in patients treated with adriamycin during the preoperative period. A single transfusion of a suspension of nonactivated allogenic bone marrow ceils markedly reduces the content of prostaglandins E in osteogenic sarcoma.