To elucidate mechanisms leading to acute myelogenous leukemia (AML), to find sensitive markers and novel targets for drug therapy, and to allow choice of suitable chemotherapy for each affected individual, we previously compared expression of mRNA from mononuclear cells of AML patients with that of normal controls using a cDNA microarray. Data from that study identified many genes that were commonly up- or down-regulated in AML cells. Of these, we report here the identification of a novel gene whose expression was increased in 27 (93%) of the 29 AML cases whose PBMC preparations include >70% leukemia cells. The gene product, localized in nuclei, showed several characteristics of transcription factors: five zinc-finger domains, a leucine zipper, and several nuclear localization signals. Its 92.5% identity in amino-acid sequence to the murine penta zinc finger protein (mPZf; gene symbol Zfp91), led us to term it ZFP91. Anti-sense oligonucleotides inhibited expression of ZFP91, suppressed cell growth, and induced apoptosis. Our results suggest that ZFP91 is likely to play an important role in cell proliferation and/or anti-apoptosis, and may serve as a molecular marker for AML.