We studied the corneal endothelial cells in 14 patients (6 men and 8 women, ranging in age from 15 to 70 years) with unilateral Fuchs' heterochromic cyclitis (FHC) by means of specular microscopy. The healthy fellow eyes of the patients served as control material. Two affected eyes had undergone an intracapsular cataract extraction before specular microscopy. In one patient, the cyclitic eye also had glaucoma. Changes of the endothelium characterized by intra- and intercellular dark bodies, larger dark defects spanning several endothelial cells and bright irregular patchy areas crossing cell borders on the specular reflex were found in all eyes with FHC. Individual cell analysis did not reveal any significant differences in the endothelial cell density, cell area, coefficient of variation for cell area, cell perimeter, cell shape and in the number of endothelial cell apices between unoperated cyclitic and healthy fellow eyes. The mean cell density was 4.9% lower in the unoperated eyes with FHC than in the control eyes. A significant negative correlation was observed between the patients' age and the cell density both in the healthy and the cyclitic eyes. On the other hand, the correlation between follow-up period and cell density was not statistically significant in the cyclitic eyes. Although FHC does not seem to accelerate significantly the age-related cell density reduction, the magnitude of the cell loss found in the two operated eyes (45.5% and 49.8%) and in the eye with glaucoma (45.2%) may indicate altered tolerance against endothelial traumas in this disease.