The retinoblastoma protein-interacting zinc finger gene (RIZ) is a zinc-finger type DNA binding protein and is postulated as a member of the nuclear protein-methyltransferase superfamily. RIZ gene encodes for two proteins, RIZ1 and RIZ2. While RIZ1 contains the N-terminal PR (PRDI-BF1 and RIZ homologous)-domain, RIZ2 lacks it. RIZ1 is now considered as a tumor suppressor. We analyzed nucleotide alteration of RIZ gene in human leukemia. The results revealed a single nucleotide polymorphism (SNP), T¹⁷⁰⁴ to A, near the conserved Rb-binding domain, leading to an amino acid change, Asp²⁸³ to Glu. Interestingly, 17 of 21 leukemia cell lines are homozygous for the T¹⁷⁰⁴ allele whereas only 2 of 20 normal subjects are homozygous for the allele. In addition, one base pair deletion in the poly (A)₉ tract in the coding region near the C-terminal zinc-fingers was identified, resulting in frameshift, in 1 out of 17 leukemia cell lines, but no mutation in samples from 15 patients with acute lymphoblastic leukemia (ALL) and 6 patients with adult T cell leukemia (ATL). In the PR or SH3 (src homology 3) domain of the RIZ gene, no mutation was found. These findings suggest that RIZ may be a possible target of structural alteration leading to leukemia.