Fludarabine uptake into cells from patients with CLL.

CLL cells were incubated as described in “Patients, materials, and methods” in the presence of 1 μM fludarabine for 10 seconds, either in an NaCl or a choline chloride medium. No Na⁺-dependent uptake was detected. Results are expressed as equilibrative uptake of fludarabine, measured in duplicate for each patient (mean ± SEM).