The responses of conventional and germ-free mice thymectomized at birth to sheep erythrocytes and to skin homografts have been investigated. Antibody production to sheep erythrocytes was depressed to an equal extent in thymectomized germ-free and conventional mice. Skin graft rejection in thymectomized germ-free mice was impaired in some cases although the extent of the impairment was generally not as extreme as it was in thymectomized conventional mice VSports手机版. The implications of the results are discussed. It is concluded that a primary consequence of thymectomy is some degree of immunological impairment but that other factors operating in the conventional state, such as bacterial contamination, endotoxins and cross-reacting antigens, act to reduce even further the number of antigen-reactive cells available in an already limited pool of immunologically competent cells. .