A panel of previously characterized monoclonal antibodies: B67.6, OKT3, OKT4, B53.4, Leu3a, OKT8, Leu2a, OKM1, M12 and B52.1 were used as a probe to assess mononuclear cells in peripheral blood (PB), lymph nodes (LN) and spleens of untreated patients with Hodgkin's disease (HD). The mean % and absolute number of T lymphocytes were significantly decreased in PB of HD patients when compared with control values. Reduction of circulating T lymphocytes reflected the selective loss of cells showing the 'helper/inducer' ('H/I') phenotype. In fact, a lower number of these cells was demonstrated in HD patients with advanced disease and, even though to a lesser extent, in those with localized disease. In contrast, decreased values of T cells with the 'cytotoxic/suppressor' ('C/S') phenotype were only found in patients with advanced disease, showing pan-lymphocytopenia. Unlike PB, LN and spleens involved by HD usually showed increased %s of T lymphocytes, especially of those possessing the 'H/I' phenotype. The displacement of T lymphocytes with 'H/I' phenotype from PB to lymphoid organs further supports the possibility of a chronic immune response against abnormal cells or unknown antigens in the affected organs of patients with HD.