Spleen is surgically removed for both non-neoplastic and neoplastic pathologies. A significant proportion of splenectomy specimens require distinguishing between reactive and neoplastic conditions (eg lymphoma). To establish a 'normal' reference range for the spleen lymphocyte subsets, fresh samples of benign, reactive spleens obtained from adult patients (N ¼ 12) and samples of normal spleen obtained from cadaveric transplant donors (N ¼ 14) were analyzed using three-and four-color flow cytometry. Study of pan-B, -T, and -NK marker expression revealed that the frequency of T cells is higher and that of B cells is lower in reactive (nonneoplastic) compared to normal (cadaveric) spleen. Furthermore, our study established a frame of reference for cell markers commonly used for immunophenotyping of lymphoma, and identified discrete lymphocyte subsets, such as early plasma cells and T cells carrying the phenotype of the NK/T subset. These results will facilitate an accurate interpretation of the flow cytometric analysis of human spleen lymphocytes.