Platelet reactivity to ADP with and without addition of CLL cells. Platelet function tests were performed on platelets from six patients with CLL. Evidence of platelet hyper-reactivity with increased area under the curve (AUC) and little decrement in platelet response to ADP from 10 μM to 2 μM was seen in three out of six patients. Some decrease in platelet reactivity was seen in all patients when 5 × 105-106 CLL cells were added to PRP and PPP. However, the decrease was minimal in one patient. P = 0.02 for 5 μM concentration, p = 0.1 for all other concentrations. However, data is partial for all concentrations except 5 μM. Of the six patients tested, four were stage 0, one stage 2, and one stage 3 disease. All had platelet counts of greater than 150 K.