A case of typical immunoblastic lymphadenopathy is described. Cell surface marker studies were performed on mononuclear isolates from peripheral blood, ascitic fluid and a lymph node biopsy and the results correlated with light microscopic findings. These data indicated that the majority of the cells in the lymph node were of T cell origin. A smaller percentage of cells could be recognized as deriving from the B cell line and it may have contained a monoclonal subpopulation. Some immunoblasts formed E rosettes and could be identified as T cells but most did not form E or EAC rosettes or bear SmIg and could not be identified as B cells. There was an associated marked increase in mononuclear phagocytes in both ascites and peripheral blood. This disease entity may represent a dual proliferation of cells originating from both B and T cell compartments with T cells predominating in the lymph node in this case.