The expression of heat-shock proteins (HSP) of the 72,000 MW family by Daudi and H9 lymphoma cells has been investigated by flow cytometry. It has been found that both heat-stressed and chronically human immunodeficiency virus (HIV)-infected lymphomas show an increased expression of heat-shock proteins (HSP). Moreover, murine monoclonal antibody (mAb) against 72,000 MW HSP was able to mediate antibody-dependent cellular cytotoxicity (ADCC) using peripheral blood lymphocytes (PBL) as effector cells. All target cells used in these experiments were efficiently lysed in the presence of anti-HSP antibody suggesting a role of membrane HSP in the elimination of stressed or infected cells.