Endocrine steroid hormones including estrogens, androgens, glucocorticoids and mineralocorticoids play clinically important and specific regulatory roles in human development, growth, metabolism, reproduction and brain function. The 11-beta hydroxysteroid dehydrogenase enzymes have key roles in the pre-receptor modification of glucocorticoids, modifications that directly regulate blood pressure, fluid and electrolyte homeostasis, as well as modulating metabolic and brain function. A recent analysis of the human genome has located a novel largely uncharacterized 11bHSD-like gene on human chromosome 19q13.3, a distinct gene from the very well characterized 11bHSD1 (human chromosome 1q32-q41) and 11bHSD2 (human chromosome 16q22) genes. Strikingly, a search in other mammalian genomes has revealed the complete absence of this third 11bHSD gene from the mouse, rat and rabbit genomes. This human 11-beta-hydroxysteroid dehydrogenase 1-like protein (HSD11B1L) gene and its encoded enzyme are completely uncharacterized for substrate specificity and detailed cellular expression pattern. The human HSD11B1L gene is encoded by 9 exons and analysis of EST library transcripts indicates the use of two alternate ATG start-sites in exons 2 & 3, and alternative RNA splicing in exon 9. HSD11B1L shares a 40% amino acid sequence homology with 11bHSD1 and the strong conservation of the NAD+/NADP+ nucleotide binding and dehydrogenase/reductase catalytic site domains.. Preliminary data demonstrates high expression of this enzyme in two human and non-human primate tissues, the ovary and brain. The endogenous substrate of this enzyme is unknown but we intriguingly show that it is unlikely to be cortisol or cortisone.