We have made a simple 15-year retrospective epidemiological study of a part of South Moravia, district Breclav, on the basis of genetic documentation of 245 congenital defects and 28 spontaneous abortions. The whole area was worked up by computer-geographical methods, and the occurrence of congenital defects was compared both in areas of severe chronic air pollution and in less contamined areas. There were three municipal areas, Mikulov, Breclav-Postorná, Velké Bilovice and their surroundings, in which an increased number of congenital defects was recorded. In the municipal area of Breclav-Postorná there was also a greater occurrence of organic solvents and phosphoric acid and a significantly higher occurrence of spontaneous abortions and at the same time a higher occurrence of heart defects.