In a survey of 450 consecutive births in Southampton a 12% incidence has been found of ophthalmia neonatorum. Bacterial pathogens were isolated from only one-third of the cases, while nonpathogens were isolated from as many cases as controls. There was an incidence of chlamydial infection of 3.7 per 1000 live births, while Neisseria gonorrhoeae could not be found. Chloramphenicol is recommended for topical antibacterial treatment, but chlamydial infection will not respond; it must be considered in 'resistant' cases, when both the neonate and the parents will need treatment with erythromycin or tetracycline.