BACKGROUND Cryopreservation is a valuable technique for storing heart valve and vascular allografts. However, the biological ramifications of cryopreservation are still unclear; therefore, using animal experiments we assessed how 'cryopreservation' influences graft allogenicity and cell viability. METHODS Thoracic aortas of Lewis rats were prepared as fresh (F) or cryopreserved (CP) grafts, and implanted into the infrarenal aorta of Lewis or Brown Norway rats (BNs). The grafts and spleens were harvested at post-operative day 7 and 28 (POD7, POD28) for analyses. RESULTS First, the systemic immune response to transplantation was estimated by mixed lymphocyte reaction analyses using spleen cells from naïve or recipient BNs. The alloreactivity of the recipients increased to 1.5 times that of the naïve BNs at POD7 and POD28, when stimulated by mitomycin C-treated Lewis spleen cells. Second, local immune response was estimated by TNFalpha, IFNgamma, and iNOS mRNA expression in the grafts by quantitative PCR, which revealed 20- to 40-fold increases at POD28 after allotransplantation. Third, endothelial cell viability was estimated by endothelial NOS mRNA expression level: it was similar and highest in F and CP grafts before transplantation then significantly decreased after both syngeneic and allogeneic transplantation. Finally, intimal hyperplasia, expressed by I/M ratio, developed over time after allotransplantation, reaching 2.5 times the thickness of F grafts before transplantation. The results of these experiments revealed no difference between F and CP grafts before and after transplantation. CONCLUSION Cryopreservation did not modify the allogenicity of vascular allografts and had minimal adverse impacts on graft cell viability.