The hypothesis that wound trauma produces either selective or total organ cell population alterations in the quantities of lympho-myeloproliferative elements in the major hematocytopoietic centers was tested. Mice were subjected to a 4% body surface skin wound on the anterior dorsum; their tissues were assayed 24 hours later for their total cellularity and proliferative potential. In wounded mice, the marrow cellularity was significantly decreased but this did not result in lower stem cell (CFU-s) and progenitor cell (CFU-c and M-CFC) quantities. However, there were significant selective and total population reductions in cells responsive to T and B cell mitogens. Splenic cellularity and stem cell quantities in wounded mice did not differ from control-treated animals. However, there were both selective and total population reductions in splenic CFU-c and M-CFC. Wounding resulted in a greater splenic T cell response to phytohemagglutinin PHA, while the responses to concanavalin-A (CON-A) were similar to controls. The splenic B lymphocyte population was specifically increased. Wounding resulted in a significant thymic hypocellularity. This was mirrored by a selective decrease in M-CFC and a total cell population reduction in response to T cell mitogens.