During ageing and senescence the aorta becomes stiffer and its elasticity is reduced. The mechanism causing this increased stiffness of the aortic wall was studied using a rat model. Ring-shaped samples were prepared from the thoracic aorta of three groups of rats aged 4.5, 14 and 27 months, representing young, adult and old animals. Analysis of the static biomechanical properties showed increased diameter (2.20 +/- 0.03 mm) and increased stiffness (4.0 +/- 0.2 mN) of aortic samples from old rats compared with adult rats (1.82 +/- 0.02 mm and 3.0 +/- 0.1 mN, respectively). The total hydroxyproline and elastin content per sample was not changed. However, the hydroxyproline content/mm2 of the aortic wall was reduced by 20% and the elastin content/mm2 of the aortic wall was reduced by 19% comparing the old with the adult rats. No differences were found in the pyridinoline concentrations between old and adult rats. The collagen- and elastin-associated fluorescence was determined as a marker of advanced glycation endproducts (AGE). Both parameters were increased in the old rats compared with the adult rats by 42% and 17%, respectively, and positively correlated with stiffness at physiological loads. A positive correlation between collagen-associated fluorescence and maximum stiffness was found as well. In conclusion, the age-related increase in stiffness of the aorta was associated with increased diameter, reduced collagen and elastin contents/mm2 of the aortic wall, increased fenestration of elastic laminae and accumulation of fluorescent material in collagen and elastin.