Previous work in this laboratory has defined two functionally distinct T cell subpopulations (viz., antigen-specific helper) and characerized some of the parameters of these subpopulations derived from the keyhole limpet hemocyanin (KLH)-primed mouse spleen. Characerization of further parameters such as relative susceptibility to tolerance induction and relative degree of specificity was not possible with the use of KLH as the antigen. In order to overcome this impediment, an experimental protocol was developed, as herewith described, to permit the study of these two T cell subpopulations in response to the antigen human gamma-globulin (HCG). This protocol qualitatively duplicates the parameters defined for the KLH system and provides an extremely useful model for the study of the response to serum proteins in the Mishell-Dutton culture system.