Anticancer drugs are good candidates for therapeutic drug monitoring (TDM) because of their high toxicity and documented exposure–response relationship for many anticancer drugs. In contrast to this, a few years ago Peterson concluded that in oncology “…plasma concentration monitoring has not proved to be of value to individualize the treatment…”. However, there are several examples where TDM in oncology has been shown to improve safety, and for some drugs, also efficacy. Examples such as 5-fluorouracil, busulfan, asparaginase, or imatinib are discussed below. It appears that there is a lack of interest of TDM and other pharmacokinetic issues in cancer chemotherapy. There is the perception that in case of toxicity or lack of efficacy switching to another drug is better than checking dose... intensity of the drug applied. However, dose individualisation based on drug concentration measurements has been shown to be advantegeous for many anticancer agents.