The transcription factor GATA-1 is a fundamental regulator of genes in haematopoietic cell lineages and belongs to a family of factors that bind to the consensus sequence WGATAR. The GATA motif was originally identified in cis-regulatory regions of globin and other erythroid-specific genes, but the range of genes controlled by the GATA factors has since expanded. Members of the GATA transcription factor family share a conserved zinc-finger DNA-binding domain, but the expression profile of each GATA factor is distinct. Here we show that a testis form of murine (m)GATA-1 messenger RNA is transcribed from a promoter located 5' to the erythroid first exon, and the remaining exons (which encode the mGATA-1 protein) are used in common by both testis and erythroid transcripts. We use an anti-mGATA-1 monoclonal antibody to show that the factor expressed in erythroid cells is the same as that found in the seminiferous tubules of murine testis. The GATA-1-expressing cells in 10-week-old testis were found only in contact with the basement membrane of seminiferous tubules, suggesting that GATA-1 regulates genes during the earliest stages of spermatogenesis.