The isolation and serial cultivation of chlamydial organisms from trachoma (Tang, Chang, Huang, and Wang, 1957; Collier and Sowa, I958) and from inclusion blennorrhoea or paratrachoma (Jones, Collier, and Smith, I959), together with the proof that these TRIC agents cause these diseases (Collier, Duke-Elder, and Jones, I958, i96o; Jones and Collier, I962) have opened the way to the development of a variety of laboratory tests that can indicate infection by Chlamydia, including those that cause trachoma and related syndromes of eye disease. Both the epidemiological study of trachoma and its control, and the individual clinical diagnosis of trachoma and other syndromes of TRIC agent infection of the eye or genital tract, have been severely hampered by the absence of sensitive diagnostic laboratory tests. There is now a variety of tests differing one from another in sensitivity and in the type of information they yield (Table I). It is now possible to provide, either for routine clinical purposes or for epidemiological studies, a service giving rapid and sensitive recognition of the chlamydial serotypes responsible (Jones, I973).