A total of 64 courses of ifosfamide (IFM) treatments for sarcoma patients were evaluated for toxic effects. A dose of 100 ml of 1/2 diluted Maalox by normal saline was instilled into urinary bladder with clump of catheter for 15 min for uroprotection instead of Mesna that was not available in Japan at that time. Forty-six courses of ifosfamide treatment in 12-16 g/m2 doses with daily Maalox instillation resulted only one hemorrhagic cystitis, while 18 courses at a dose of 6-10 g/m2 of IFM without Maalox eventuated in 5 cases of hemorrhagic cystitis. Forty-six courses of ifosfamide treatment at a dose of 12-16 g/m2 (mean dose of 14.4 g/m2) for 5 to 6 day continuous infusion were evaluated also for myelosuppression, nephrotoxicity, neurotoxicity, and other toxicities. Myelosuppression was acceptable, although the absolute neutrophil count of the 80% course was below 500. No patient showed neurotoxicity characterized by confusion or somnolence. No course resulted in abnormal serum creatinine elevation, although two of 46 courses caused an abnormal decrease of creatinine clearance. One patient had arrhythmia that required medical treatment after 5 courses of IFM treatment.