Cervical lymph nodes of rabbits were congested for 24 hours, 7 days, and 14 days by occlusion of the nodal veins, efferent lymphatics, or both. The lymph nodes were examined by histologic and morphometric methods, and the results were compared with findings in control nodes. The present study demonstrated that the vascular sinus transformation (VST), observed first in human lymph nodes, is reproducible experimentally. Complete occlusion of both the veins and lymphatics led to a marked increase in volume of the nodes and often to total necrosis of their parenchyma. Incomplete occlusion of the veins combined with complete occlusion of the lymphatics or complete occlusion of the lymphatics alone resulted in VST as early as 7 days after the operation. In the first stage of VST, proliferation of the subendothelial tissue accompanied by proliferation of blood capillaries was noted. The proliferation started from the capsular side of the marginal sinus and from the trabecular side of the intermediate sinuses. Subsequently, the sinuses transformed into a framework of channels resembling blood capillaries. Without occlusion of the efferent lymphatics, VST did not develop. Complete or incomplete occlusion of the veins combined with complete occlusion of the lymphatics resulted in a pronounced thickening of the capsule, sclerosis of the medullary sinuses, depletion of lymphocytes in the nodal parenchyma, and cavernous dilation of the medullary sinuses. After occlusion of the lymphatics alone these changes were less extensive. Occlusion of veins alone caused only moderate thickening of the capsule and slight sclerosis of nodal parenchyma, but no VST. Total necrosis of the parenchyma occurred only after combined complete occlusion of nodal veins and lymphatics.