Of 120 individuals suffering from follicular conjunctivitis, with or without keratitis, 56 had epidemic keratoconjunctivitis caused by adenovirus type 8. The remaining 64 patients had keratoconjunctivitis produced by several different viruses, including herpes simplex, adenoviruses types 3, 7, 8, 16, 21, and 29, and others. Positive viral cultures were difficult to obtain after the first week of illness in most viral infections. Serologic tests were far more successful in indetifying causative agents. Hemagglutination-inhibition tests in adenovirus infections proved to be fast, accurate, and more sensitive than other serologic tests. Among the epidemic and nonepidemic adenovirus groups, the degree of corneal involvement in the infections appeared to be correlated with the level antibody against the infectious agent. Patients with low antibody titers had more severe keratitis than those with high titers. This correlation was true for both the epidemic and non epidemic patients.