Forty-three patients, ranging in age from 7 to 30 years (median age, 17 yr), with primary osteogenic sarcoma (OS), confirmed by biopsies and with no evidence of metastatic disease at the time of diagnosis, received T-7 chemotherapy for an average of 4 months before surgery, including high-dose methotrexate (HDMTX) and citrovorum factor rescue (CFR) (median, 7 courses), and 1 course each of bleomycin, cyclophosphamide, and dactinomycin, and adriamycin. At the time of definitive surgery, the surgical specimen showed a good histologic response to chemotherapy (grade III or IV response) in 29 (67%) of 43 patients and a poor histologic response (grade I or II response) in 14 (33%) of 43 patients. Among those who responded well, no patient relapsed, as all received a complete course of preoperative and postoperative chemotherapy for more than 5 to over 28 months after the initiation of treatment (medium, 13 mo). Among those who responded poorly, 6 of 14 patients relapsed with pulmonary metastases (a thoracotomy was beneficial to 1), 4 of 6 patients are alive with disease, and 1 patient died of progressive disease. On retrospective analysis, we observed that good and poor responders did not differ in the distribution of sex, age, race, primary site of disease, or histologic subtype of OS. An elevated alkaline phosphatase level that returned to normal under preoperative chemotherapy indicated a good response. Neither the 24-, 48-, and 72-hour serum MTX levels nor the fluid intake and urinary output during 3 days that followed HDMTX with CFR correlated significantly with tumor response. Based on our studies with this form of therapy, we concluded that the response of OS to preoperative chemotherapy is of prognostic value.