Normal hematopoietic stem cells proliferate and differentiate in the presence of growth factors such as interleukin-3 (IL-3). Transformation can alter their growth factor requirements, the ability of the cells to differentiate, or both. To identify genes that are capable of transforming hematopoietic cells, IL-3-dependent cell lines, isolated from retrovirus induced myeloid leukemias, were examined for viral insertions in proto-oncogenes and in common sites of viral integration. Five of 37 cell lines contained proviruses in a common viral integration site termed the ecotropic virus integration 1 site (Evi-1). The integrations were correlated with the activation of transcription from the locus. Sequencing of cDNA clones and genomic clones demonstrated that the integrations had occurred near or in 5' noncoding exons of a novel gene. The sequence of the cDNA clones predicts that the gene product is a 120 kd protein that contains two domains with seven and three repeats of a DNA binding consensus sequence (zinc finger) initially described in the Xenopus transcription factor III A (TFIIIA). This represents the first demonstration of the retroviral activation of a gene encoding a zinc finger protein and the first implication for a member of this gene family in the transformation of hematopoietic cells.