A low rate of catabolism of cortisol by lymphocytes correlates with high sensitivity of the cells to the steroid and causes them to die at a greater rate than control samples. Since lymphocytes of patients with chronic lymphocytic leukemia respond to treatment with glucocorticosteroids and are cortisol sensitive, we attempted to see whether their capability to catabolize cortisol differs from that of normal lymphocytes. No difference was found between the two groups of cells with regard to the pattern of cortisol metabolites. However, the lymphocytes of the chronic lymphocytic leukemia groups showed a total cortisol catabolism per cell that was significantly lower than that of the control group. Patients with low lymphocyte count in peripheral blood showed a relatively higher cortisol metabolism by lymphocytes per cell than those with high counts.