T-lymphocyte subsets from 27 severely burned patients and 32 controls were analysed using monoclonal antibody immunofluorescent staining and flow cytometry. Compared to normal controls, burn patients showed a remarkable reduction in absolute number of CD3-lymphocytes in the 48 h following injury, which was accounted for by a decrease in both CD4 and CD8 subsets. Activated lymphocytes, as defined by expression of CD25, CD69 and CD71, were significantly increased in burned patients. Additionally, a moderate increase in lymphocytes bearing simultaneously CD4 and CD8 was observed in some burned patients. The expression of CD11c, CD49a and CD54, members of the integrin family of cell surface molecules, was shown to be increased on lymphocytes from thermally injured patients. We conclude that thermal injury produces a profound T-cell lymphopenia with features of extensive T-cell activation, and postulate that depletion of circulating T-cells could be related with the expression of surface adhesion molecules and cell redistribution from blood to the tissues.