The trapping of lymphocytes occurring at different times after a single injection of Propionibacterium granulosum was studied. Labeled syngeneic lymphocytes injected into Propionibacterium-treated recipients showed a different pattern of localization from that observed in untreated animals. A pronounced decrease in homing to the lymph nodes and spleen and an increase in localization in the liver were found. The extent of trapping in the liver corresponded to the increase in weight of this organ. Whole-body irradiation with 400 R, used to achieve autologic lymphocyte depletion, did not change the localization of labeled cells. However, macrophage damage caused by silica resulted in diminished trapping in the liver in Propionibacterium-treated animals and increased accumulation of labeled lymphocytes in the spleen and lymph nodes.