beta-L-3'-Fluoro-2',3'-didehydro-2',3'-dideoxycytidine (L-3'-Fd4C) is a potent and selective antiretroviral nucleoside with activity against lamivudine-resistant human immunodeficiency virus type 1 (HIV-1) and hepatitis B virus (HBV) in vitro. The pharmacokinetics of L-3'-Fd4C were characterized in three rhesus monkeys given single intravenous and oral doses. A two-compartment open model was fitted to the plasma and urine data. Plasma concentrations declined in a biexponential fashion with an average beta half-life of 12.45 h and central and steady-state volumes of distribution of 0.43 and 1.90 liters/kg, respectively. The average systemic and renal clearance values were 0.23 and 0.08 liters/kg, respectively, and the apparent mean terminal half-life of the oral dose was 12.5 h. The serum concentrations exceeded the 90% effective concentration value for lamivudine-resistant and wild-type HIV-1 after oral administrations. A large variation was observed in the oral bioavailability, which ranged from 15 to 31%. To determine whether the bioavailability may be improved by using a basic buffer solution, the oral dose was repeated to the same animals in a sodium bicarbonate solution. The bioavailability of L-3'-Fd4C administered with sodium bicarbonate was not significantly different from the bioavailability when the oral dose was administered in the absence of buffer (P = 0.49), suggesting that further development of this compound may warrant other approaches, such as development of a prodrug to improve its oral absorption.