SOX proteins are a family of transcription factors with high-mobility-group DNA-binding domain (HMG box) homologous to SRY, which are implicated in embryogenesis. Xenopus Sox17 alpha, Sox17 beta, and Sox3 are reported to negatively modulate the WNT - beta-catenin - TCF signaling pathway. Here, human SOX17 gene fragments were identified in human genome draft sequences by using bioinformatics, and SOX17 cDNAs were isolated by using cDNA-PCR. Human SOX17 was found to encode a 414-amino-acid protein with a HMG box, which was homologous to SOX18 and SOX7. SOX17 gene, consisting of 2 exons, was located in human chromosome 8q12-q13 region. SOX17 mRNAs of 2.5- and 2.2-kb in size were detected in adult heart, lung, spleen, testis, ovary, placenta, fetal lung, and kidney. In normal gastrointestinal tract, SOX17 mRNA was preferentially expressed in esophagus, stomach and small intestine than in colon and rectum. SOX17 mRNA was almost undetectable in human cancer cell lines HL-60, HeLa S3, K-562, MOLT-4, Raji, SW480, A549, G-361, and also in 66 cases of human primary tumors derived from various tissues, except one case of primary cervical cancer. This is the first report on molecular cloning and characterization of human SOX17.