In 21 patients with unilateral glaucomatocyclitic crisis (Posner-Schlossman syndrome) the central corneal endothelium was photographed with a clinical specular microscope. In each patient the endothelial cell density was determined in both the affected and the contralateral healthy eye. In patients who had had several attacks of P-S the endothelial cell density was lower in the affected eye than in the healthy eye (16 cases). 4 patients seen after the first attack and 1 of 3 patients after the second attack had the same cell density in both eyes. Thus, loss of endothelial cells seems to be due mainly to the recurrent attacks of elevated pressure. The role of the inflammatory changes occurring in eyes with the P-S syndrome, especially keratic precipitates, is discussed.