Increasing evidence points to the possible risks of delayed effects upon prenatal exposure to chemicals; the evaluation of such effects may pose serious problems to clinicians, epidemiologists and toxicologists. In fact, several systems (e.g., nervous, excretory) show important developmental processes well after the organogenetic period, up to the postnatal phase; accordingly, these are also expected to be sensitive targets of developmental toxicants, resulting in impairment of the function and/or functional reserve. This review describes the effects of several groups of drugs on the functional maturation and histogenesis of the kidney (e.g., aminoglycosides, angiotensin-converting enzyme inhibitors, indomethacin) and brain (e.g., anticonvulsivants, antiretroviral compounds, benzodiazepines) upon exposure in utero of humans and laboratory animals. The available data stress the importance for risk assessment of an adequate knowledge of both developmental biology and mechanisms of toxicity. The design of developmental toxicity studies should allow an evaluation of targets most relevant for a given drug (or group of drugs); moreover, the analysis of functional development should receive the due attention within the safety assessment of chemicals.