Patients with B-cell chronic lymphocytic leukaemia (B-CLL) have an increased susceptibility to infection. Quantitative abnormalities of T-cells have been previously reported in B-CLL, although the relationship between such abnormalities and the incidence of infection still remains to be established. We therefore enumerated lymphocyte subpopulations in 22 patients with B-CLL grouped according to the number of infective episodes in the previous three years. No significant differences were found between the patient groups and the mean number of T-cells subsets (helper, suppressor, suppressor-inducer and suppressor effector) or NK cells, but patients with frequent infections were found to have significantly higher CD5+ B-cell counts. Thus, we confirm that T-cell subpopulations are numerically altered in patients with B-CLL, but found that such changes are not predictive of susceptibility to infection. Our results however suggest that the malignant B-cells may exhibit immunosuppressive activity.