The immunological events which occur in lymph nodes situated regional to renal allografts have been studied by collecting lymph from these nodes and monitoring the changes in its cellular and humoral antibody content. Simultaneously, reactions occurring in the renal allograft and in lymph nodes distant to the graft were also monitored in the lymph from these organs throughout the life of the graft. Large basophilic lymphoid cells appeared first in lymph from the renal allograft at around 48 hr postgrafting, whereas these cells did not appear in the lymph from the regional node until 80–100 hr after the graft was installed. Lymphoid blast cells were not seen in any significant numbers in lymph from nodes siutated at a distance from the graft. The first detectable antibody was produced by the regional lymph node between 110 and 175 hr postgrafting, and in other undetermined sites within the next 80 hr. Antibody was not synthesized in any detectable amounts by the graft or by lymph nodes situated at a distance from the graft. The antibody which was present in the lymph from the regional node was produced primarily by fixed cells which remained in the node, and very little antibody was produced by the lymphoid cells which migrated from the node in efferent lymph. The cells in the lymph from the renal allograft produced only small amounts of immunoglobulin. Cells present in lymph from the renal allograft and in lymph from the regional lymph node actively synthesized and secreted significant amounts of nonimmunoglobulin proteins which were separated on Sephadex G-200 columns into peaks which coincided with 19S, 7S, and 4S proteins. The identities and biological activities of these proteins have not yet been determined.