13 patients with Hodgkin's disease (HD) previously treated, 9 of whom were long-time (more than 2 yr) off-therapy, were studied for peripheral blood lymphocyte response to interleukin 2 and for lymphocyte subpopulations by means of in vitro cultures and monoclonal antibodies. The aim of the study was to ascertain the role played by interleukin 2 in the impaired cell-mediated immunity of HD patients. The results show a response of peripheral blood mononuclear cells of HD patients to either the T cell-specific polyclonal mitogens PHA and Con A or to the T cell-dependent, although B cell-specific, PWM, most significantly decreased compared to the normal response. As far as the interleukin 2 involvement in HD is concerned, our study suggests: an impaired endogenous interleukin 2 production by T lymphocytes, a most probable deficiency of the interleukin 2 receptor (Tac) expression and 3) a decrease of the number and/or of the function of NK cells no longer responsive in vitro to interleukin 2. The phenotypic analysis of peripheral blood mononuclear cells showed a slight decrease of total T cells (T3+), of the helper/inducer subset (T4+) and of the T4+/T8+ cells ratio. Our data seem to support the rationale for a therapeutical approach with interleukin 2 in controlled clinical trials also in HD patients, according to the experiments in progress in solid tumor patients.