The main objective of this study was to evaluate the intensity and character of the inflammatory reaction caused by an innovative polyester-polyurethane vascular prosthesis implanted into the abdominal aorta of 9 Beagle dogs aged 1-3 years. At 6 and 12 months post implantation the prostheses were removed and tissues samples were examined using 2 methods: histology and immunohistochemistry (IHC). Histology slides stained with hematoxylin and eosin (H&E) were evaluated for the intensity of inflammation by observing the density of inflammatory cells and graded 1 to 4 (1- light inflammation, 4 – severe inflammation). The pro-inflammatory mediator tumor necrosis factor-alpha (TNFα) and two anti-inflammatory mediators, interleukin 1 receptor antagonist (IL1ra), and interleukin 10 (IL10), were also assessed in the tissue samples by IHC methods. Mean (n=5) inflammation grade in H&E slides at 6 months post-implantation (6Mpost) was 2 and mean (n=4) inflammation grade at 12 months (12Mpost) was almost 3. IHC staining showed that TNFα and IL1ra in tissue samples obtained from 6Mpost dogs were expressed at the same intensity indicating equal pro- and anti-inflammatory cytokine levels. However, in the 12Mpost tissues TNFα was expressed more intensely than IL1ra and IL10. Moreover, in 2 dogs at 12Mpost, there were signs of infection assessed on the basis of neutrophil infiltration in the prostheses. In conclusion, the assessment of pro-inflammatory mediators such as TNFα and anti-inflammatory mediators, such as IL1ra and IL10, can help to interpret the intensity of the inflammatory process directed at synthetic prostheses.