Comparison of deoxynucleotide level after forodesine therapy. Patient no. 5 received 2 courses of forodesine 40 mg/m² day 1, then twice daily for 4 days. Samples were assayed after infusions 2, 4, 6, and 8. Intracellular concentrations of dCTP (•), dTTP (▵), dATP (□), and dGTP (▴) were quantitated by DNA polymerase assay and are plotted after the first (A) and second (B) courses.