The effect of social confrontation stress on the normal distribution of blood T cells into lymphoid organs and some other body tissues was studied. Social stress was induced by placing a male Fischer 344 (F334) rat into the home cage of a resident opponent. 51Cr-labeled blood T cells isolated from syngeneic donor, were intravenously injected into recipients immediately before confrontation. The accumulation of 51Cr-labeled T cells in the spleen, mesenteric and cervical lymph nodes 24 h after injection was about 30% lower in socially stressed than in control males. Substantially higher localization was observed in the bone marrow of socially stressed males.