The amniotic fluid cells of 2 patients with rubella at the 18th week of pregnancy were obtained during therapeutic abortion and examined with a transmission and a scanning electron microscope (SEM). In comparison with amniocytes of healthy women, those of rubella patients showed marked alterations, consisting of lack of heterochromatin, almost complete disappearance of the electrondense cytoplasmic layer and membrane changes. The membrane damage was clearly demonstrated by SEM and was expressed by a decrease in the number and size of microvilli. Although more experience is needed for evaluation of the ultrastructure of the amniotic fluid cells in rubella patients, these findings may serve as an additional tool for the intrauterine diagnosis of rubella.