Factor VIII acts as an essential compound of the tenase complex of the coagulation system. Herein we report the cDNA of the rat factor VIII. The rat cDNA comprises 6777 nucleotides and encodes a protein of 2258 amino acids, 61 amino acids less than mouse and 92 amino acids less than human factor VIII. The over-all identity compared to human cDNA is 61% on the cDNA and 51% on the amino acid level. In cDNA, highest levels of sequence identity can be observed in the A and C domains (ranging between 68% and 73%), whereas B domain and the small acidic regions are more divergent (34% - 49%). Compared to mouse and human most sites for posttranslational modifications such as sulfatation and glycosylation as well as thrombin and protein C cleavage sites are conserved in rat. Alternative transcripts lacking exon 17 and/or comprising additional 26 bp due to alternative splicing of exon 20 were found. Furthermore, 13 polymorphisms (seven in exon 14, one in exon 20, 23, 24, and 25, two in the 3' UTR) three of which lead to an amino acid exchange could be detected. Our findings might provide new insights into the structure-function analysis of the factor VIII protein and might prove useful for future animal models addressing the function of factor VIII.