Summary Adenoviruses were isolated from 106 of 204 patients diagnosed as having epidemic keratoconjunctivitis (EKC) who attended the National Taiwan University Ophthalmology Clinic in 1958 and 1959. Serological studies on some of the patients from whom virus was not isolated suggest that most, if not all, were adenovirus infections. Of the adenovirus types isolated, type 8 was by far the most common (72%), while type 4 was the only other type isolated with any frequency (13%). In addition, types 2, 3, 7, 10, 11 and several adenoviruses not types 1 to 18 were isolated. Of the patients in whom follow-up examinations were carried out, 14 of 18 from whom type 8 was isolated developed subepithelial punctate keratitis (SPK), while only 3 of 11 with other types developed this pathognomonic sign. In all, SPK was found in 32 patients including 1 from whom type 4 was isolated, 1 with type 11 and 2 with unclassified types. Type 8 was isolated from throat swabs and from the eyes of 13 patients. The average length of incubation time to isolate 129 strains of type 8 was 27 days as compared to averages of 13 to 20 days for the other types isolated. Conjunctival swab specimens were as good or slightly better than scrapings were for the isolation of adenovirus. Most EKC cases occurred in the late summer and fall. All ages were involved, but SPK was not seen in patients under 13 years. Detailed clinical findings are reported on a portion of the patients. Most cases were unilateral, had conjunctival petechial hemorrhage and preauricular lymphadenopathy. Only a few had pharyngeal or generalized symptoms. The clinical severity was similar, irrespective of virus type isolated.