A peculiar hereditary corneal disease seen in one pedigree is presented. The disease manifests itself as transient attacks of kerato-endotheliitis. These attacks last from a few days to some weeks. Clinically, corneal oedema and endothelial guttata-like changes with very slight anterior chamber reaction can be seen; after many attacks there may be permanent opacities in the stroma. Endothelial specular photography during an attack reveals dramatic changes: large black nonreflecting areas between quite normal-looking hexagonal cells. Also between the attacks and among family members who have no clinical corneal disease, changes in the endothelium: black spots in the centres of endothelial cells and marked pleomorphism, are to be seen. Among the family members a high incidence of collagen diseases was found.