This study has the following main purposes: (1) To compare the clinical efficacy of mesna given by the approved intravenous regimen of 20% of the ifosfamide dose at 0,4 and 8 hours to the proposed intravenous and oral dosing regimen in which intravenous mesna at 20% of the ifosfamide dose is given at 0 hour and mesna tablets at 40% of the ifosfamide dose are administered at 2 and 6 hours, in the prevention of ifosfamide-induced hematuria. (2) To compare the safety and tolerability of these two regimens in the prevention of ifosfamide-induced hematuria. (3) To determine urine pharmacokinetic measurements in a limited number (N=12) of patients.