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. We have recently identified a novel largely uncharacterized 11bHSD-like gene on human chromosome 19q13.3, a distinct gene from the very well characterized 11bHSD1 and 11bHSD2 genes. Strikingly, a search in other mammalian genomes has revealed the complete absence of this third 11b-like HSD gene in the mouse, rat and rabbit genomes. The human 11-beta-hydroxysteroid dehydrogenase 1-like protein (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 splicing in exon 9. We have detected expression of this enzyme in tissue samples from the brain, ovary and testis. Analysis of cell-type specific expression by immunohistochemistry localizes cytoplasmic expression to ovarian Granulosa cells, testis Leydig and sertoli cells, and somatotroph cells in the anterior pituitary from non-human primates and the sheep. The endogenous substrate of this enzyme is unknown but we intriguingly we show that it is very unlikely to be cortisol or cortisone.