Employing various ablative and reconstituting procedures on inbred chickens, an investigation into the role of thymus (T) cells in the antibody response will be undertaken. It is postulated that there are at least two types of T cells, one synergistically and one antagonistically involved in the response. By selective removal of the antagonistic population it is anticipated that the response to an antigen will be enhanced. The response will be measured not only as the production of specific antibody but also as the synthesis of non- specific immunoglobulin. A number of parameters of T cells will be studied in order to define differences between helper T cells and suppressor T cells. These will include development, life span and distribution in the peripheral lymphoid organs. It is postulated that the suppressor T cells play an important role in the control of the normal response especially against self- constituents. This postulate will be tested by attempting to delay a normally occurring autoimmune phenomenon through the introduction of excess suppressor T cells.