Chronic B-lymphocytic leukemia (B-CLL) cells may be regulated by immune functions. In an attempt to analyze such functions, helper factors (IL-1 alpha, IL-1 beta and IL-6), T-cell products (sCD4 and sCD8) and sIL-2R and beta 2-microglobulin were measured in serum of patients at different stages of the disease. Patients were classified as having monoclonal lymphocytosis of undetermined significance (MLUS), stable or progressive B-CLL respectively. A significant, but modest, increase of IL-1 alpha was found in B-CLL as well as in MLUS patients whereas IL-6 levels were increased in MLUS only. sCD8 levels were increased both in MLUS and B-CLL but augmented sCD4 concentrations were found statistically significant only in progressive B-CLL. beta 2-microglobulin and sIL-2R were related to the extent of the monoclonal B-cell fraction. The data indicate an increased T-suppressor activity in both MLUS and B-CLL patients and a selective increase of helper T-cell activity in progressive B-CLL. A possible immunoregulatory influence of helper T cells on disease progression is discussed.