['Ageing impairs endothelial function such as the regulation of vascular tone. The release of nitric oxide (NO), which has a potent vasodilator effect and antiatherosclerotic property, is decreased in the aorta of aged rats. Exercise training, however, has been reported to increase the expression of endothelial NO synthase (eNOS) in the aorta of young rats. In aged rats, it is not known whether the expression of eNOS is altered by exercise training. We hypothesized that exercise training would improve the ageing-induced decrease in eNOS expression in vessels, and examined the messenger RNA (mRNA) and protein expression of eNOS in the aorta of sedentary-young rats (sedentary-young group; 4 months old), sedentary-aged rats (sedentary-aged group; 23 months old), and swim-trained aged rats (training-aged group; 23 months old, swimming training for 8 weeks, 5 days week(-1), 90 min day(-1)).', 'Body weight was significantly lower, and citrate synthase activity in the epitrochlearis muscle was significantly higher in the training-aged group compared with the sedentary-aged group. The mRNA expression of eNOS in the aorta was significantly higher in the training-aged group than in the sedentary-aged group, while it was significantly lower in both the sedentary-aged and training-aged groups than in the sedentary-young group. The expression of eNOS protein in the aorta was also significantly higher in the training-aged group than in the sedentary-aged group, while it was also significantly lower in the sedentary-aged group, but not in the training-aged group, than in the sedentary-young group.'] Does exercise training improve ageing-induced decrease in eNOS expression of the aorta?