Whole blood %CD38 by CLL cells predicts cell division in coculture. Comparison of the capacity of CLL cells with a high (≥ 20%) and low (< 20%) %CD38 to undergo division after coculture with activated autologous T cells. Significantly more CD38^hi CLL cells underwent at least one division compared with the CD38^lo group. Statistical significance was determined by the unpaired t test.