A high number of activated cytotoxic T lymphocytes (CTL) in Hodgkin's disease (HD) biopsy specimens is related to an unfavorable clinical outcome, suggesting that resistance of the Hodgkin and Reed-Sternberg (H-RS) cells to CTL-mediated killing is an important pathogenic factor in HD. bcl-2 and defective p53 are known to inhibit apoptosis induced either by CTLs or by therapy. The purpose of this study was to use immunohistochemical techniques to analyze whether differences in expression of these proteins in H-RS cells in primary biopsy specimens from 78 patients with HD were related to clinical outcome and to assess the number of CTLs in those cells. Cases with H-RS cells mostly staining positive for bcl-2 but negative for p53 had a poor prognosis (55% 5-yr survival). In the group of patients whose H-RS cells had low positivity for both p53 and bcl-2, the 5-year survival was 90%. p53 expression in a high percentage of H-RS cells was invariably related to a 100% 5-year survival, irrespective of bcl-2 expression. Biopsy specimens from patients with a fatal clinical outcome, in which few H-RS cells expressed p53 and many H-RS cells expressed bcl-2, contained relatively many activated CTLs. These data demonstrate that the combination of expression of the apoptosis-regulating proteins p53 and bcl-2 in the H-RS cells can be used as a prognostic marker for HD, and they indicate that resistance to apoptosis of H-RS cells is an important pathogenic mechanism. Our data also support the hypothesis that in patients with a poor prognosis, apoptosis-resistant H-RS cells might be selected for by the presence of many activated CTLs.