Immunophenotypic analysis of simultaneous specimens from different sites from the same patient with malignant lymphoma The assumption that immunophenotypic characteristics of different specimens obtained simultaneously from the same patient remain unchanged has rarely been evaluated. Using flow cytometry, we reviewed our experience of 29 patients with non Hodgkin's lymphoma (NHL). From these patients, 60 simultaneous specimens taken from the peripheral blood, bone marrow, effusions, fine needle aspirates from lymph nodes or cerebrospinal fluid were studied. In 26 out of 29 patients, the immunophenotype in the different specimens was identical. In one patient with unclassifiable low-grade B-NHL, immunophenotyping showed additionally a CD38 expression in the effusion which was not seen in the bone marrow. In one patient with mantle cell lymphoma, expression of CD10 in the lymph node was noted which was lacking in the peripheral blood. In the remaining patient with unclassifiable low-grade B-NHL, CD23 expression was noted in the lymph node but not in the peripheral blood. This retrospective study suggests that discordant antigen expression in samples from different body sites within the same patient is a rare event.