The generation of human CEACAM1 transgenic mice is an important model to demonstrate equivalence in function of the murine and human gene orthologs. Since pathogens that utilize human CEACAM1 as their receptor do not recognize murine CEACAM1, such a model is essential to study their pathogenesis. Furthermore, in order to demonstrate that CEACAM1 specific anti-pathogen vaccines are effective, the model must mimic the human tissue specific pattern of CEACAM1 expression. Thus, our approach was to generate transgenic mice that expressed the entire human CEACAM1 gene rather than a cDNA for CEACAM1. Although we attempted to generate several lines using BAC clones that spanned different regions of chromosome 19 encoding the CEACAM1 gene, only a single line that actually expressed the protein was generated. Given the large number of variables that affect both integration, expression, and transmission of a gene, the reason for this result is unknown. Fortunately, the BAC2-12 line obtained transmitted the transgene from the founder mouse to F1 and F2 generations and demonstrated the expected frequency for heterozygotic expression in subsequent generations. Furthermore, human specific splice forms were found in three major tissues (liver, intestine and kidney) of known CEACAM1 expression and tissue staining for human CEACAM1 demonstrated the expected staining pattern, namely at the lumen of epithelial cells.