An outbreak of keratoconjunctivitis is described which involved at least 186 people; adenovirus type 8 was identified in 50 of the cases. Topical human fibroblast interferon was assessed in a double-blind, placebo-controlled study in which 34 patients participated. Seventeen of the 34 trial patients yielded adenovirus type 8; three were infected with adenovirus type 7. The outbreak was curtailed by control of infection measures: principally careful hand-washing by medical personnel between cases and by discouraging attendance of new cases at the Eye Infirmary. Consequently the trial numbers are small. In addition there was a wide interpatient variation in the severity of infection. Therefore it was not possible to make any statistically valid conclusions concerning the recovery rate of patients receiving interferon or placebo.