3'-Azido-2', 3'-dideoxyuridine (AZDU, AzddU, CS-87) has been shown to have potent anti-HIV activity in vitro. However, the compound exhibits a relatively short half-life and incomplete oral bioavailability in humans. In an effort to improve the pharmacokinetic properties of AZDU, prodrug 3'-azido-2',3'-dideoxyuridine-5'-O-valinate hydrochloride (AZDU-VAL) was synthesized by the esterification of 5'-OH function in AZDU. The objective of this study was to investigate the biotransformation and pharmacokinetics of AZDU-VAL along with its antiviral parent compound AZDU following intravenous and oral administration to rats. Adult male Sprague-Dawley rats were administered AZDU or AZDU-VAL by intravenous injection or oral gavage. Concentrations of AZDU-VAL and AZDU were determined by HPLC. Pharmacokinetic parameters were generated by area-moment analysis. The bioavailability of AZDU after oral administration was approximately 53%. The terminal phase half-life of the nucleoside analogue ranged between 0.6 h after intravenous administration and 1 h following oral administration. In vivo the prodrug was rapidly and efficiently biotransformed to yield AZDU following intravenous and oral administration. The apparent availability of AZDU was virtually complete following oral administration of prodrug AZDU-VAL averaging 101%. The bioavailability of AZDU following intravenous administration of AZDU-VAL averaged 106%. In summary, the disposition of AZDU was dose dependent over the dose range of 25-100 mg/kg. Renal clearance and steady state volume of distribution were lower at the higher dose level. Prodrug AZDU-VAL demonstrated improved oral bioavailability as evidenced by complete absorption and efficient bioconversion to AZDU. The results suggest that AZDU-VAL may be a promising prodrug for the delivery of AZDU.