Autoantibodies binding 60 kD Ro (or SS-A) are commonly found in patients with systemic lupus erythematosus and Sjögren's syndrome. While many studies have examined the autoimmune response directed against this RNA-protein, its function is still uncertain. As part of a broad effort to better understand animal models of anti-Ro autoimmunity we have characterized the murine 60 kD Ro gene. Southern blot analysis of mouse genomic DNA suggests that the 60 kD Ro gene is a single copy gene. The complete sequence of the gene was determined from three overlapping genomic lambda phage clones (GenBank accession number AF065398). The murine 60 kD Ro gene spans approximately 23 kb and consists of 8 or 9 exons. DNA sequence analysis revealed the presence of multiple B1 repetitive units. It maps in synteny with the human 60 kD Ro gene. Therefore, the isolation and characterization of the 60 kD Ro gene will be instrumental for future studies on protein function and the role this protein plays in the development of autoimmune responses.