Since the thalidomide (Contergan) tragedy about 30 years ago the induction of prenatally-induced morphological or functional defects has been an area of extensive research. Risk assessment of prenatally-induced adverse health effects is still a difficult task from both experimental data as well asfrom observations in humans. In the contributions to this book three major aspects are dealt with: - Quantitative extrapolations of experimental data to the situation possibly relevant for man. - The significance for a risk assessment with respect to man of minor or rare structural abnormalities observed in experimental studies - The future need to assess congenital dysfunctions (e.g. of the hormone or the immune system) beside the present evaulation of structural defects. Limitations as well as gaps of the present knowledge in this area of basic and applied research are pointed out. Since the results of prenatally-induced lesions may manifest themselves not only pre- but often not before late postnatally, numerous aspects of structural and functional abnormaldevelopment must be studied in experimental and clinical investigations.