A wide variety of organisms from the environment invade the preputial cavity of rams. Various of these organisms can be isolated from the deeper parts of the male genital tract, and especially from the accessory glands. Some of the bacteria present in the sheath can be stimulated to migrate to the deeper parts of the genital tract by injections into the host animal of luteinizing-hormone- releasing-hormone and injections of pregnant mare serum gonadotrophin. The increased levels of luteinizing hormone and follicle-stimulating hormone in surgically prepared cryptorchids also stimulate migration of the organisms. The natural mode of development of genital infections in rams is formulated as follows: The preputial cavity of a ram becomes invaded by various organisms through contact with the environment. When, under the influence of systemic hormonal stimulation, the genitalia undergo development, suitable conditions are created for the migration of some of the bacteria in the sheath to the deeper-lying organs of the genital tract such as the vesicular seminales, epididymides and testes. In these organs the bacteria can possibly initiate a pathological process.