Adverse environmental conditions, both biological and social, during gestation and postnatal development may interfere with gene controlled, time and space determined programme of ontogenic processes and induce irreparable defects. These epigenetic variables also include drugs which are prescribed in ever increasing amounts in late pregnancy, during labour and neonatal care to save the lives of high-risk fetuses/neonates. Drug administration in the perinatal period which is characterized by intensive cytodifferentiation and receptor formation in the brain and immune system, may initiate disorders on a cellular/subcellular level and give rise to functional defects which become apparent during later maturation or even in adulthood as various deviations of neuro-psychoimmunocompetence. This functional teratogenic risk is especially high in drugs with receptor-mediated effects (psychotropics, hormones) since the majority of receptors necessary for their action develop in the perinatal period. The functional teratogenic potential of three perinatally applied drugs (dexamethazone, phenoterol, diazepam) was evaluated using model experiments in rats and compared with the outcome of clinical pilot follow-up studies.