Immunophenotyping of frozen lymph node sections from seven patients with morphologically defined angioimmunoblastic lymphadenopathy (AILD) was performed with a panel of 20 monoclonal antibodies (MoAb). MoAb for identification of dendritic reticulum cells showed remnants of follicular structures in all cases. In four cases these 'burnt out' follicular structures were associated with clusters of polyclonal B-cells. Vascular proliferation and small amounts of intercellular collagenous fibrils were reliably revealed by MoAb CIV22 against basement membrane collagen. Cellular infiltrates of T4+ cells prevailed in four cases, of T8+ cells in one case. In one case conventionally identified blasts were of T- and B-cell origin. Expression of cell proliferation associated nuclear antigen identified by MoAb Ki-67 was present in more than 25% of lymph node cells in three patients with fatal outcome, but in less than 10% of cells in two patients with a better clinical course. Therefore MoAb Ki-67 may represent a valuable prognostic marker in AILD.