We report the first use of amnion epithelium for prenatal diagnosis. Prenatal diagnosis of recessive epidermolysis bullosa atrophicans generalisata gravis Herlitz type can at present be achieved with safety by detailed ultrastructural analysis of fetal skin. Because of the close developmental origin of amnion and skin, which has been elucidated by the recent development of anti-amnion antibodies against dermo-epidermal junction antigens and by their abnormal binding in epidermolysis bullosa skin, there is presumably some morphological relationship between amnion epithelium and skin. In a comparative study of extra-embryonic tissues, we found ultrastructurally complete hemidesmosomes in all 24 investigated normal amnion samples from gestational weeks 15-27, but not in 7 reflected chorion samples from weeks 16-22. The results of placental chorion samples were not reliable. Amnion of 5 fetuses affected with epidermolysis bullosa atrophicans generalisata gravis revealed only hypoplastic hemidesmosomes, the same defect as in the respective skin. In a recent case where unfortunately only non-skin material was available, a positive prenatal diagnosis of epidermolysis bullosa atrophicans gravis Herlitz was performed from the amnion material. The diagnosis was confirmed by investigation of the fetal skin after termination. Investigation of amnion membranes is therefore an alternative for prenatal diagnosis of epidermolysis bullosa atrophicans gravis Herlitz in certain cases. The possibility and limitations of the general use of amnion for prenatal diagnosis are discussed.