In order to assay the efficacy of newly synthesized antiviral compounds, pyrimidine analogs, pharmacokinetics of those were established as compared with already marketed zidovudine. Zidovudine (15, 20, 25 and 35 mg/kg), LJ142 (18.52 mg/kg) and LJ143 (15, 18.52 and 30 mg/kg) were administered orally and intravenously in rats, blood samples were collected post-injection(i.e., for 360 min) at appropriate time intervals. Those were analyzed by HPLC with UV detection at 265 nm. Pharmacokinetic parameters $(C_{max},;T_{1/2},;MRT,;AUC,;AUMC,;Vd_{SS},;Cl_t)$ were calculated. AUCs of zidovudine and LJ143 following I.V. dosing of $15{sim}25;mg/kg;and;15{sim}18.18;mg/kg$ were dose-independent. However, AUCs of zidovudine and LJ43 following I.V. dosing of $25{sim}35;mg/kg;and;18.18{sim}30;mg/kg$ were dose-dependent. The relative bioavailability of zidovudine, LJ142 and LJ143 following oral administration were 61.94, 46.44 and 78.24%, respectively.