A cast was taken of the rabbit mesenteric lymph node by injecting Mercox resin into the lymphatic vessel, then excising the lymph node and removing the tissue with 20% KOH. The resulting cast was observed under an SEM. The outer surface of the cast, corresponding to the marginal sinuses, consisted of an arrangement of dome-like structures of about 1mm in diameter. A cross section of the cast showed that the marginal sinuses penetrate deeply into the cortex down to the trabecular and cortical sinuses, surrounding the secondary lymphoid nodules and connecting with the medullary sinuses. The cast of the diffuse lymphoid tissue showed numerous structures like tangled strings of beads, each bead with a maximum diameter of 40u and minimun of 10u. These were lymph pathways running through the reticulum cell network between the marginal sinuses and medullary ones. The cast of the primary lymphoid nodules showed a coral-like or irregular menbranous structure of 5u in thickness just under the dome-like marginal sinuses. Blind ending lymph vessels filled with resin were demonstrated at the center of the secondary lymphoid nodules. The cast of the medullary sinuses showed tortous tubes of 100-150u in diameter branching from or anastmosing with each other. The fine coral-like structures were also seen around the medullary sinuses.