The US Food and Drug Administration (FDA) has proposed new labelling regulations that describe alternative approaches for providing additional information to support labelling a drug, already approved for use in adults, for use in children. Therefore, the study of drugs in paediatric populations may now be encouraged. Paediatric pharmacokinetic studies are an important part of these trials. This action by the FDA may help resolve the ethical and technological concerns about the performance of clinical trials in children, and may render paediatric clinical trials more feasible. Most investigations in children are opportunistic in nature and their design is often constrained by a requisite noninvasive approach. Appropriately applied population-based techniques for both pharmacokinetic and pharmacodynamic data analysis may represent the most robust approach for generating a sufficiently large and accurate database for the use of new or old drugs in paediatric patients. Accordingly, this information, which is crucial for paediatric labelling of any drug product, must be obtained in infants and children if we are to truly individualize therapy for paediatric patients. The funding of 6 Pediatric Pharmacology Research Units by the US National Institutes of Health, and guidelines for application of pharmacokinetic methods to children may further contribute to the performance of paediatric clinical trials.