Peripheral venous blood lymphocytes of 10 untreated B-CLL patients at stages Rai 0-III and of 10 healthy individuals were studied. In B-CLL the absolute number of T lymphocytes present in peripheral blood was similar to that in healthy controls; however, the ratio of T lymphocyte subpopulations in B-CLL was changed in favour of TG cells, the absolute number of which was found to be increased. In B-CLL DNA synthesis of the TG cells in response to PHA stimulation was more intense than in healthy individuals. These observations are discussed in the light of the conflicting reports on the numerical and functional changes in B-CLL T-cells.