The TRIC-Taiwan-1-1958 strain of elementary body virus isolated from a trachoma patient on Taiwan has been proven capable of reproducing trachoma by experimental inoculation of six human volunteers. Virus material derived from the seventh passage in embryonated hen eggs caused the clinical picture of trachoma in every inoculation, even at the dilution of 10–4 of infected yolk sacs (approximately 1 EID50). There was a similar clinical picture with each inoculation beginning with an acute follicular conjunctivitis which progressed for 4 months and then persisted with chronic changes until 9 months when treatment was begun. The illness was generally more acute than would be expected in natural trachoma. That trachoma was reproduced was shown by the involvement of the cornea with epithelial keratitis and pannus, and by the occurrence of gelatinous follicles and eventual cicatrization of the conjunctiva. These clinical findings were supported by repeated demonstrations of typical inclusion bodies of Halberstaedter-Prowazek from conjunctival and even corneal cells, by repeated reisolation of elementary body virus in egg yolk sacs, and by the development of complement-fixing antibody with a "specific" trachoma antigen in each volunteer. Control inoculations with adenovirus type 4 and normal yolk sac showed different clinical and laboratory findings. Experimental trachoma vaccine was given to three of the volunteers to study its effect on the course of illness. An antibody response to the vaccine was demonstrated and there was a modification of disease in the volunteers receiving vaccine. While the three volunteers who received placebo each developed cross-infection of their uninoculated eye and had an acute reactivation of the bilateral disease after 1 to 2 months of antibiotic eye ointment therapy, the vaccinated volunteers remained free of infection in uninoculated eyes and showed no relapse after ointment therapy. Treatment with sulfamethoxypyridazine, a sulfa drug with prolonged action, proved to be an effective and relatively simple method of therapy for experimental trachoma.