Tissue sections embedded in paraffin and fixed in formalin from 65 patients with Hodgkin's disease (HD) were examined for the presence of heat shock protein 70 (HSP70) and Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) using avidin-biotin immunoperoxidase complex technique. The staining results in Reed-Sternberg (R-S) cells and their variants were evaluated independently. HSP70 expression was found in R-S cells in 55 cases (85%) of HD examined and the frequency of HSP70 positive cases was significantly higher than that of HSP70 negative cases (P < 0.01). This protein was present in pathogenic cells in 9/12 cases (75%) of lymphocyte predominant Hodgkin's disease (LPHD), 21/27 cases (78%) of mixed cellularity Hodgkin's disease (MCHD), 10/10 cases (100%) of lymphocyte depleted Hodgkin's disease (LDHD) and 15/16 cases (94%) of nodular sclerosing Hodgkin's disease (NSHD). The association between HSP70 expression and HD thus appeared to be more frequent in patients wish LDHD and NSHD subtypes, although examples of HSP70-positive tumors were found in all histological subtypes. Studies of non-neoplastic lymphoid tissues demonstrated that centroblasts (large lymphocytes in germinal centers) were constantly positive; occasional histiocytes revealed variable reactivity for.