We examined 22 patients in active phase of Hodgkin's disease (HD), 12 patients in complete clinical remission and 16 healthy subjects for their responsiveness to anti-CD3 stimulation as measured by CD25 antigen expression on peripheral blood mononuclear cells (PBMC) and production of CD25-IL-2R alpha. Simultaneously, the serum levels of soluble interleukin 2 receptor alpha (sIL-2R alpha) were estimated. Our studies indicate that PBMC in patients in active phase and in clinical remission have impaired ability to express CD25 antigen after stimulation with anti-CD3 monoclonal antibody. Similarly, the levels of sIL-2R alpha in culture supernatants were significantly lower in both groups of patients: in active phase and clinical remission compared with the controls. In contrast, the mean serum level of sIL-2R alpha was significantly higher in active phase of the disease compared to that found in patients in clinical remission and controls. Our studies suggest that sIL-2R alpha, derived from PBMC, is not the source of increased levels of sIL-2R alpha found in the sera of patients in active phase of HD. Their synthesis and secretion/shedding most probably takes place in the involved tissues.