A retrospective investigation was performed on the significance of dose intensity in preoperative chemotherapy for osteosarcoma. In this paper, we studied 29 patients, who had classical stage II-B osteosarcoma and received preoperative treatment consisting of high dose methotrexate (HD-MTX) and/or cisplatinum (CDDP) between 1985 and 1991. Preoperative dose intensity was calculated in the following two ways. 1. Total dose of MTX and CDDP administered during initial five weeks: MTX (g)/10/m2 + CDDP(mg)/100/m2 2. Dose intensity of MTX and CDDP from initiation of treatment (I) to resumption of postoperative chemotherapy (R): MTX (g)/10/m2 + CDDP (mg)/100/m2 / days from (I) to (R)/ideal period of new regimen (63 days) Continuous disease free survival rate (CDFR) was significantly higher in the group receiving preoperative chemotherapy at higher dose intensity (> 3.0). Supplementary administration of adriamycin (ADR) to CDDP/MTX was not favorable in the preoperative stage, because it put off the following therapy and diminished the dose intensity. Since July 1989, we have tried a short intensive preoperative chemotherapy regimen: weekly two cycles of CDDP 100 mg/m2 intravenously, followed by weekly two cycles of HD-MTX 10g/m2. Surgery was scheduled six weeks after beginning treatment, and postoperative chemotherapy was started three weeks after surgery. Twenty patients have been treated by this regimen to date. All patients remain disease free, and six are CDF beyond 24 months.