For certain types of advanced cancers patients may be given a combination of an anthracycline and a taxane for chemotherapy treatment. Despite the fact that a mixture of anthracyclines and taxanes may be administered simultaneously to patients and that accurate measurement of drug levels during chemotherapy is proven to be more beneficial to patients, currently no chromatographic method exists for the measurement of any anthracycline and taxane drugs in a single assay. It would be useful to carry out therapeutic drug monitoring (TDM) in order to assess how the patient is metabolising the drugs and to see whether the dosage is working or should be altered. Such information during therapy can be a very important clinical tool for the oncologist, enabling them to change dosage or even drug regimen on an individual basis for patients, improving outcome in the long run. This thesis describes the development of the first on-line SPE-LC-UV method capable of quantifying both drug types in a single assay.