An online SPE-LC method that can determine both anthracyclines and taxanes simultaneously in human serum samples is reported. The entire method of extraction, separation and UV detection was achieved online by column switching between an SPE column (Biotrap 500 (20 x 4 mm)) and an analytical column (Zorbax XDB C18, 150 x 4.6 mm, 5 jam) with a 23 min total cycle time. The method is linear (r(2)>0.998) over the range of 0.5-25 mu g/mL. The analytes of interest are retained on the SPE column with good recovery (84-117%), while proteins and other serum components elute to waste. This online cleanup is much faster (150 s) and less manual than traditional off-line extraction methods. Using 0.1 mL spiked serum samples, the LOQ was 0.5 mu g/mL. Intra- and inter-day precision were acceptable (<= 15% RSD) at and above the LOQ. The method was applied to the analysis of serum samples from patients undergoing chemotherapy with these agents.