In order to evaluate the preventive efficacy, safety and usefulness of mesna (Sodium 2-mercaptoethane sulfonate) against ifosfamide-induced urinary disorders, a placebo-controlled double-blind comparative study was performed. Ifosfamide was administered by intravenous drip infusion at a daily dose of 2 g/m2 for 5 consecutive days, and mesna was intravenously administered at 20% of the ifosfamide dose, three times daily for 5 consecutive days. The results obtained are as follows. (a) Of 101 accrued patients, 91 patients were evaluated consisting of 45 for the mesna group and 46 for the placebo group. There was no intergroup difference in the number of the evaluated cases and patient characteristics. (b) Micturition pain and feeling of residual urine graded as moderate or severe were not observed for the mesna group, but were observed for the placebo group with incidences of 19.6% (9/46) for micturition pain and 15.2% (7/46) for feeling of residual urine; the intergroup differences in the appearance of these urinary symptoms were statistically significant (P = 0.0003 for micturition pain; P = 0.0009 for feeling of residual urine). The incidence of hematuria graded as moderate or severe was 6.7% (3/45) in the mesna group, which was significantly lower than the 32.6% (15/46) in the placebo group (P = 0.0008). (c) No side-effect attributable to mesna was observed. (d) A judgment of "useful" was obtained in 80.0% (36/45) of the patients treated with mesna, which was significantly higher than the 34.8% (16/46) of the patients treated with placebo (P = near 0). On the basis of the above results, we conclude that the preventive efficacy, safety and usefulness of mesna against ifosfamide-induced urinary disorders have been well demonstrated in this study.