Direct immunofluorescent staining of conjunctival cells is, at present, the most sensitive method for the detection of TRIC agents. Detailed evidence for the specificity of the method is provided. By means of immunofluorescent staining, TRIC agents can be detected in specimens from the eye of many individuals who do not exhibit current clinical activity of trachoma or inclusion conjunctivitis. Examples from spontaneously infected individuals and from experimental infection in volunteers support the belief that latent infection with TRIC agents is commonplace and may occupy an important role in the natural history of these infections which involve many millions of people. We propose that the clinical signs of activity in trachoma and inclusion conjunctivitis do not adequately reflect the presence of the infectious agent. Future considerations of diagnosis, treatment and control must include subclinical infection and latency of TRIC agents.