The classical definition of clinical pharmacology is the study or the knowledge of the effects of drugs in humans. The activities of a clinical pharmacologist can vary from country to country, usually ranging from involvement in clinical trials, especially fundamental pharmacodynamic studies, to studies of pharmacokinetics and drug metabolism, to pharmacogenetics. Most clinical pharmacologists outside industry are in hospitals or university hospitals and research centres. In addition to research, this implies teaching of clinical pharmacology, and interacting with other medical staff: in the field of research, giving advice on clinical trials methodology and often managing a therapeutic drug monitoring centre. Some clinical pharmacologists have clinical departments with beds or consulting offices. Can there be another role for the clinical pharmacologist that would increase his or her usefulness for the medical community? Adverse drug reactions (ADRs) are remarkably complex events, related to drug effects, patient characteristics (background diseases, genetics), and drug/disease interactions. Evaluation of ADRs requires understanding of drug mechanisms and interactions, and of disease diagnostics, especially in the discussion of alternative diagnoses. This implies expertise as a pharmacologist and a clinician. In addition, because not all adverse reactions or interactions are in the Summary of Product Characteristics, and because problems arise long before they report in the literature, it is necessary for the clinical pharmacologist to have knowledge of ongoing regulatory processes, in addition to having access to the published literature. Helping clinicians cope with individual patient problems will also improve the clinical pharmacologist's integration into the healthcare process.