A single nucleotide polymorphism at TP53 codon 72 means that two alleles exist: A1 (proline residue, Pro72) and A2 (arginine residue, Arg72). The Pro72 variant of p53 has a lower apoptotic potential. We found that allele A1 was more frequent in patients with chronic myeloid leukemia (CML) than in controls, and among CML patients who had no cytogenetic response than among responders.