A high-performance liquid chromatographic method was developed for the quantification of doxorubicin derived from PEGylated liposomal doxorubicin (Doxil) and its major metabolite in human plasma. This method utilizes Triton X-100 to disperse the liposome, followed by a protein precipitation step with 5-sulfosalicylic acid. Analytes in the resultant supernatant are separated on a Discovery RP amide C(16) column (250 x 3 mm I.D., 5 microm) using an isocratic elution with a mobile phase consisting of 0.05 M sodium acetate (pH 4.0) and acetonitrile (72:28). The retention times for doxorubicin and the internal standard daunorubicin were 4.8 and 10.1 min, respectively. The column eluate was monitored by UV-visible detection at 487 nm. The determination of doxorubicin was found to be linear in the range of 1.0 ng/mL to 25 microg/mL, with intra-day and inter-day coefficients of variation and percent error < or =10%. The recovery of doxorubicin from plasma was >69.3%, with a liposomal dispersion efficiency of >95.7%. Our analytical method for free and PEGylated doxorubicin in human plasma is rapid, avoids organic extractions, and maintains sensitivity for the parent compound and its major metabolite, doxorubicinol.