The purpose of this thesis is to investigate the effects of baicalein, an antioxidant, on the bioavailability and pharmacokinetics of Doxorubicin (DOX) in rats. Thus, DOX was administered intravenously (i.v.; 10 mg x kg(-1)) or orally (p.o.; 50 mg x kg(-1)) with or without oral baicalein (0.3, 1.5 and 6 mg x kg(-1)). In the presence of 1.5 and 6 mg x kg(-1) of baicalein, the total area under the plasma concentration-time curve from time zero to time infinity (AUC) and the peak concentration (Cmax) of DOX were significantly greater and higher, respectively, than those of the control. Consequently, the absolute bioavailability (AB) of DOX in the presence of baicalein was 3.5-4.4%, which was significantly enhanced compared with that of the control group (2.2%). The relative bioavailability (RB) of DOX was 1.20 to 1.96 times higher than that of the control group. Compared to the intravenous control, the presence of oral baicalein increased the i.v. AUC of DOX and other pharmacokinetic parameters were not significantly affected. The enhanced bioavailability of oral DOX by oral baicalein may be due to the inhibition of both P-glycoprotein (P-gp) and the cytochrome P450 (CYP) 3A subfamily by baicalein in the intestine and/or liver. This result suggests that the development of oral DOX is feasible by combination with baicalein that would be more convenient than the i.v. dosage forms. Furthermore, since the present study raises the awareness about potential drug interactions by concomitant use of DOX with baicalein, the dosage regimen of DOX should be taken into consideration, if this result is confirmed in clinical studies.