Immunological functions of 9 non-splenectomized and 8 splenectomized patients with Hodgkin's disease were studied before and after treatment. The two groups compared well with regard to age, clinical and immunological findings at diagnosis and observation time. When retested, all patients had enjoyed an unmaintained complete remission for 2 to 5 years following total nodal radiotherapy. After therapy, total lymphocyte and T-lymphocyte counts decreased in non-splenectomized patients but remained unchanged in splenectomized patients. The blood lymphocyte DNA synthesis after activation by concanavalin A or pokeweed mitogen persisted at the same low level after treatment. The delayed skin hypersensitivity and the lymphocyte activation by PPD antigen were restored in several patients in both groups. The IgM concentration decreased after therapy independent of splenectomy. The IgA level was low in non-splenectomized patients. Splenectomy seems to protect from the therapy-induced lymphocytopenia. No alterations of immunoglobulins and blood lymphocyte functions could be ascribed to splenectomy.