“…The yolk-sac technique, however, is now known to be less sensitive than cell culture for Chlamydia isolation (Gordon, Dressler, and Quan, 1967;Gordon, Harper, Quan, Treharne, Dwyer, and Garland, 1969). Other studies have been made of special groups: women in whom chlamydial ocular disease was known to be present or who produced offspring with chlamydial ocular disease (Dunlop and others, 1964;Dunlop, Freedman, Garland, Harper, Jones, Race, du Toit, and Treharne, 1967), and women who were known to be sexual contacts of men with NSU (Dunlop and others, 1972;Oriel and others, 1972). The incidence of genital chlamydial infection in other groups is not known.…”