This thesis has looked at the effect of feeding a particulate antigen (Sheep red blood cells) or a soluble antigen (human gamma globulin) on both the local and systemic immune response to that antigen. Sheep red blood cells (SRBCs) were given orally to mice using two different feeding protocols and their systemic antibody response and cell-mediated immunity to subsequent parenteral immunisation was examined. In both feeding schedules cell-mediated immunity (CMI) was easier to suppress than antibody production. Using one feeding protocol, attempts were made to transfer this suppression of CMI, Several doses of soluble antigen (HGG) were used and one regime giving long-lasting profound suppression of delayed-type hypersensitivity (DTH) was used to examine DTH in the fed animals and in recipients of various cell populations from fed animals. The protocol used was to feed HGG at 1 mg/ml for at least fourteen days. While parenterally immunised animals could transfer DTH to syngeneic recipients using peripheral lymph node lymphocytes (PLNs), fed animals were unable to do this whether or not they were parenterally immunised after feeding but prior to cell transfer. On the other hand, neither mesenteric lymph node lymphocytes (MLNs) nor Peyer's patch lymphocytes (FPs) from parenterally immunised animals could transfer DTH while MLNs from fed mice could. Peyer's patch cells from fed mice caused a delayed reaction in recipients but this was not statistically significant from the negative control. This pattern of transfer of DTH from gut-associated lymphoid tissue of fed mice was not altered following parenteral immunisation prior to transfer, Intra-epithelial lymphocytes from both orally and parenterally immunised mice could transfer DTH. This was not due to the different preparative procedure used. Finally, isolated lymphocytes from mesenteric lymph node, peripheral lymph node, gut epithelium and gut lamina propria were examined for their ability to undergo antigen and mitogen-induced proliferation after oral and/or parenteral immunisation. Lymphocytes from the gut proved difficult to culture in vitro even in the presence of various mitogens. The implications of the presence of DTH reactive cells in the gut mucosa are discussed with reference to what role this may play in normal and abnormal immune responses in the gut.