Peldesine (BCX 34) is a potent, competitive, reversible and orally active purine nucleoside phosphorylase (PNP) inhibitor with IC50s of 36 nM, 5 nM, and 32 nM for human, rat, and mouse red blood cell (RBC) PNP, respectively. Peldesine is also a T-cell proliferation inhibitor with an IC50 of 800 nM. Peldesine has the potential for cutaneous T-cell lymphoma, psoriasis and HIV infection treatment.