This paper reports a study of the locomotor behaviour of the lymphocytes from 17 patients with chronic lymphocytic leukaemia (CLL). The cells were studied both immediately after separation from blood and after culture for 24 to 48 h with a range of growth activators. Cells direct from blood were tested for polarization in fetal calf serum (FCS 20%), phorbol myristate acetate (PMA 10(-7)M) and colchicine (10(-5)M). The polarization of lymphocytes from CLL patients with high white cell (WBC) counts (greater than 10 X 10(9)/litre) was very poor in FCS and PMA, though the cells from about half of these patients responded well to colchicine. The response of cells from patients with low white cell counts was the same as that of controls. The growth activators, PHA (1 micrograms/ml), anti-CD3 antibody (OKT3 2.5 ng/ml), Cowan strain Staphylococcus aureus (SAC; 1.5 X 10(7)/ml) and PMA (10(-8)M) induced an increase in the proportion of locomotor lymphocytes from controls and from CLL patients with low white cell counts during 24 h of culture. Cells from patients with high white cell counts showed very little increase in locomotor forms in any activator including PMA and the B cell mitogen SAC. This defect was seen in both polarization assays and collagen gel invasion assays. The findings suggest that CLL lymphocytes have a defect of locomotion demonstrable at two levels: (a) the cells fail to respond by polarizing immediately upon stimulation; colchicine treatment reverses this defect in some cases; (b) they also fail to acquire locomotor capacity during culture with activators of growth.