The CD1 molecules are a family of β₂-microglobulin-associated glycoproteins with strong structural homology, but weaker sequence homology, to the MHC class I antigens. In contrast to the classical class I antigens, CD1 molecules exhibit restricted tissue expression (cortical thymocytes, dendritic cells, a subset of B cells and some intestinal epithelial cells), and are nonpolymorphic. Five CD1 genes have been identified in humans , two in the mouse and several in other mammalian species (Calabi et al, 1991). CD1 expression has also been detected by immunohistological techniques in the cow, sheep and pig. The MHC class I-like structure of CD1 and the expression on classical antigen presenting cells of the immune system has pointed to a role for CD1 in antigen presentation. Indeed, evidence has been accumulating over the past few years to support this view, with several reports suggesting that CD4^-8^- T cells in particular may be able to recognise nonclassical presentational elements including MHC class Ib molecules such as TLa and Qa, as well as CD1. Most recently, CD1b molecules on human monocytes have been demonstrated to restrict the response of CD4^-8^- T cells to antigens derived from M.tuberculosis (Porcelli et al, 1992). Previous studies on the ovine CD1 family have involved the use of monoclonal antibodies to assess tissue expression and distribution, and biochemical analyses of the ovine CD1 antigens. However, no studies have been carried out to investigate ovine CD1 at the molecular level. Therefore, a human CD1C α3 probe was used to screen several sheep thymocyte cDNA libraries. The HCD1B-like cone SCD1A25 was isolated from a foetal thymocyte library. A homologous probe comprising the α3/TM/CYT domains from this clone was derived by PCR amplification and used to identify a further three ovine clones-SCD1B-42, SCD1B-52 and SCD1T10.