Five term placentae from pregnancies at risk of infantile neuronal ceroid-lipofuscinosis (INCL) were studied electron-microscopically to determine if diagnostic cytoplasmic inclusions could be detected in this tissue. In 4 placentae no inclusions were found, and the infants born from these pregnancies have developed normally, the shortest observation time being 15 months. In the fifth placenta numerous cytosomes pathognomonic of INCL were found in the amniotic cells and the endothelium of the capillaries of the chorionic villi. The diagnostic significance of this finding was confirmed by the presence of typical inclusions in the autonomic ganglion cells and other cells in a rectal mucosal biopsy specimen of this male infant at the age of 3 months. Electron microscopic study of chorionic villus biopsy specimens appears to be a promising possibility for prenatal diagnosis of INCL.