Fourteen patients were followed up with slit-lamp, noncontact, and wide-field specular microscopical examination for anterior segment changes during unilateral attacks of keratouveitis due to varicella zoster virus (VZV). Ten patients had severe keratouveitis. Their affected eyes presented nonreflecting endothelial changes in different phases of the disease. The first non-reflecting changes suggesting virus endothelitis were observed at the onset of keratouveitis. These changes later recurred for several months. When the corneal oedema had subsided, the mean endothelial cell density of the affected eyes was on average 15.3% lower (p less than 0.01) than in the healthy fellow eyes. During early uveitis transient high intraocular pressure (IOP) developed in 5 patients. Patients with severe disease and an episode of high IOP had a 20.2% lower cell count in the diseased than in the healthy fellow eye. During the follow-up interstitial keratitis developed in 2 cases and focal iris atrophy in another 2. Four patients presented with mild keratouveitis. The posterior cornea and endothelial cell density in this group remained unchanged.