The dose-limiting urotoxicity of the oxazaphosphorines (t1/2 = 4-15 h) is due to renal elimination of metabolites such as acrolein. The occurrence of hemorrhagic cystitis can be safely prevented by the concomitant use of i.v. or oral 2-mercaptoethanesulfonate sodium (DCI MESNA; Uromitexane). The bioavailability of oral MESNA is in the range of 20-50% and its unpleasant taste severely limits patient compliance. Due to the short half-life of MESNA (approx. 40 min) a regular fractionated or continuous administration is mandatory. In 6 healthy volunteers we have studied the pharmacokinetics of urinary MESNA elimination for the assessment of MESNA bioavailability after i.v. and s.c. drug administration. MESNA was given at doses of 400 mg for i.v. and s.c. bolus injections and 800 mg for continuous s.c. administration by a portable infusion pump. For the s.c. route an isotonic solution was prepared. The total amount of urinary thiols was assessed by the Ellman method (photometric reading at 412 nm). Total elimination of i.v. MESNA was 83.2 +/- 3.4% of the dose administered. The respective results for s.c. bolus and s.c. continuous drug administration were 81.9 +/- 3.4% and 79.4 +/- 3.6% of the dose. Continuous administration theoretically will provide optimal uroprotection from short term (hemorrhagic cystitis) and long term (bladder fibrosis and cancer) toxicity.