It is estimated that only a small portion (less than 2 %) of the congenital anomalies is attributed to chemicals including drugs. However, developmental toxicity of pharmaceutical drugs has the following characteristics. 1. A considerable number of new compounds are introduced into market every year after reproduction tests in animals. 2. Drugs are intentionally administered, often subchronically with a relatively high dose. They are given after consideration that potential benefits to a pregnant mother outweigh possible hazards to both mother and her unborn child. 3. Congenital anomalies induced by drugs can be prevented if they are withdrawn from the market. Therefore, a more strong administrative judgement is requested in evaluating the hazards to human development as compared to not only environmental chemicals but also physical and biological develop-mental toxicity agents. In this short review, first, methods for detection of developmental toxicity of drugs are commented. Significance of animal studies and basic principles for evaluation of human survey (case reports and epidemiological studies) are discussed. Secondly, critical reviews are presented on some drugs which have recently become the subjects of controversial discussion. These include Bendectin, vaginal spermicides, diethylstilbestrol, progestogens and anticonvulsants. Bendectin episode may be a typical example how difficult to treat the tetatogenicity of drugs as the social problem. Other topics of special concern are adverse effects of drugs therapeutically used for the fetus itself and of preconceptional chemical exposure to not only mothers but also fathers. Finally, various problems on the balance between benefits and risk of drug usage in pregnancy are commented and the author's opinion is expressed how doctors and patients should consider the use of drugs in reproductive age in order to clarify the etiology of congenital anomalies by drugs and their prevention.
