In 93 patients (mostly sporadic cases) with suspected EKC an infection with adenoviruses was proved by virological and serological methods in 54 cases. Types 8, 3, 7, 19, 4, and 14 were found in 38, 6, 5, 3, 1, and 1 cases respectively. 33 out of 48 patients with clinically typical EKC had an infection with type 8. From the patients without adenoviral infection, the absence of which having been proved by extensive serological tests, 7 showed a typical EKC. The symptoms considered as relatively typical (hyperemia and oedema of the plica and caruncle, subepithelial corneal infiltrates) were not confined to patients with adenovirus infection; thus they cannot be considered as characteristic for this group of viruses. The results indicate the need for a specific diagnosis in cases of suspected EKC, which should include virus isolation from conjunctival swabs as well as the demonstration of antibody titer rises by various serological tests. EKC is to be considered as a clinical and epidemiological rather than as an etiological entity.