In 47 patients who had undergone splenectomy (31 post-trauma and 16 elective), the percentage levels of T and B lymphocytes, and the T lymphocyte subsets and circulating immune complexes were studied in peripheral blood and correlated with residual splenic function evaluated by means of the pitted red cell count. The T and B lymphocyte levels in splenectomized patients did not differ significantly from those in controls, while OKT8+ lymphocyte levels were significantly higher both after post-trauma and elective splenectomy; there was no significant difference between the two groups of splenectomized patients. Circulating immune complexes were significantly higher both after post-trauma and elective splenectomy only with the C1qBA and C1qSP methods, while there were no differences between splenectomized patients and controls with the KgBSP method. None of the three methods showed significant differences between post-trauma and electively splenectomized individuals. The pitted red cell levels were significantly lower in post-trauma splenectomized patients with respect to electively splenectomized individuals and 22% of post-trauma splenectomized patients had pitted red cell values within the range compatible with the presence of splenosis. The immunological alterations detected did not correlate with the pitted red cell levels, nor were they less evident after post-trauma splenectomy or in patients with pitted red cells compatible with splenosis: this suggests that the occurrence of splenosis is not sufficient to prevent these alterations. Finally, since in our study the average distance from the operation was 5 yr, it is likely that these alterations can be considered as being stable.