Terminology for the morphologically simiilar psittacosis, lymphogranuloma venereum (LGV), trachoma organisms has been con fused. They have been referred to as the PLT group, the Bedsonia and more recently the Chlamydia. The latter terminology would appear to be gaining official sanction and in creasing use. Two species have been recog nized: Chlamydia trachomatis and Chlamy dia psittaci. These have been differentiated on the basis of glycogen-containing inclu sions and sulfa drug sensitivity of C. tracho matis. 1 The trachoma and inclusion conjunc tivitis organisms belong to the species C. tra chomatis and have been referred to as TRIC organisms. 2

On the basis of our immunologie and bio logical classification studies, we have devel oped terminology and tentatively grouped TRIC organisms and other species C. tra chomatis strains. TRIC organisms are sepa rated from other C. trachomatis strains by their ability to cause typical follicular con junctivitis in primates. Among TRIC strains, there are two major divisions. One is organisms isolated from all areas of the world that have endemic trachoma. These have only been isolated from the eye and all such agents have been shown to belong to immunologie Types A, B, and C in our mouse toxicity prevention test (MTPT) classification. 3 These organisms cause mild follicular conjunctivitis in the monkey eye and 100 to 1000 EID50 are required to infect