The first 2 parts of this report have been presented in a previous communication.1 Intravenous mechlorethamine hydrochloride caused no observable pathological changes in the normal rabbit eye. Treatment with intravenous mechlorethamine of infectious tuberculous uveitis in nontuberculin-sensitive rabbits showed only a temporary inhibition of the inflammatory process. Part 3, the conclusion of this project, is similar to Part 2 with the exception that the rabbits used in this last experiment are tuberculin sensitive. The ocular response of the sensitive animal is different from that of the nonsensitive animal. Larger doses of bacilli are necessary to produce lesions. When an appropriately larger dose is given, 24 to 36 hours after the injection of the bacilli into the anterior chamber, there is a sharp inflammatory response—the typical picture of nongranulomatous iritis. This initial reaction is a bacterial hypersensitivity reaction produced in a hypersensitive animal by the tubercle protein in the inoculum.