If you are found to be eligible to take part in this study, on Day 1, Cidofovir will be put into your bladder through your foley catheter. The catheter will be clamped for 2 hours to keep the drug in your bladder. After 2 hours, the catheter will be unclamped. If you were receiving bladder irrigation as therapy for your hemorrhagic cystitis, this will be restarted.