The use of fluorescein-conjugated monoclonal antibody (Syva, UK) provided a rapid reliable diagnostic test for Chlamydia trachomatis in conjunctival samples from 100 adults with acute follicular conjunctivitis and seven babies with suspected chlamydial ophthalmia neonatorum. Elementary bodies (EBs) were seen in smears from 11 of the adults, and culture confirmed C. trachomatis infection in nine of them. Both tests were positive with specimens from four of the neonates. No specimens from either group of patients produced a negative result in the smear test but a positive result by culture. However, the two adult patients with chlamydial ophthalmia who had negative cultures but were EB-positive had both had prior topical tetracycline therapy.