H-2 linked genetic control of antibody responsiveness has been demonstrated for a number of synthetic and natural immunogens, including the synthetic polypeptide (T,G)-A--L and staphylococcal nuclease. The purpose of this study was to determine whether a) similar genetic control of cell mediated immunity in vivo could be demonstrated for (T,G)-A--L and nuclease; b) such cell mediated immunity is generated by T- or B-lymphocytes; and c) cell mediated immunity can be demonstrated for T-cell independent synthetic polypeptide immunogens which are under genetic control. A footpad assay involving vascular leakage at a site of inflammation has been developed to study murine cell mediated immunity to the synthetic polypeptide GAT. In the current study mice injected with the above-mentioned immunogens were challenged in one bind footpad with the immunogen, followed by an intraperitoneal injection of I125-labelled serum albumin. One day later the mice were killed, and the relative amounts of isotope leakage in the control and experimental feet were compared. Adoptive transfers of T- and B-lymphocytes from immunized mice were also made in untreated hosts.