Positron emission tomography (PET) provides the oncologist with information on tumour diagnosis, and treatment response monitoring. Mathematical modelling of tissue data, and online plasma radioactive metabolite profiling, enables important tissue kinetic parameters relating to the uptake, distribution and washout as well as arterial input function to be derived. The resultant kinetic data allow for not only diagnosis but also the assessment of therapeutic response endpoints. These endpoints can be used to measure specific therapeutic effects. This novel application of PET can provide information that is often difficult to measure in the intact animal or patient. The pharmacokinetics of radiolabelled N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA), temozolomide and 5-fluorouracil (5-FU) are described.