The immunological and functional consequences of splenectomy in patients with severe trauma are still controversial. In addition to the higher incidence of bacterial infections, including the post-splenectomy sepsis syndrome, alterations of the peripheral blood mononuclear cells (PBM) have been described in patients after splenectomy. We studied the effects of splenectomy in severely injured patients on the number of PBM subsets 30-80 (median 55) months after splenectomy. Compared to a control group of patients with a similar age and a similar severity of trauma there was no significant difference between splenectomized and non-splenectomized patients regarding the absolute and relative numbers of monocytes, B cells, T cells, CD4+ cells, CD8+ cells, NK cells, CD57+/CD8+ cells and CD4+/CD8+ cells. The CD4/CD8 ratios were within the normal range. In two trauma patients without splenectomy the CD57+/CD8+ cells were found to be elevated to 635 and 513 cells/mm3 compared to less than 100 CD57+/CD8+ cells in controls. Except for a slight thrombocytosis in the splenectomized patients (p less than 0.05) the differential cell count showed no difference between both groups. Our data thus suggest that, in a controlled study, splenectomy has little if any effect on peripheral blood mononuclear cell subsets, while severe trauma on its own may have a profound long term effect on T cell subsets in some patients.