Sedentary aging is associated with endothelial dysfunction and nitric oxide (NO) impairment. The aim of the present study was to assess the effects of regular physical exercise on nitrite/nitrate (NOx) concentrations and microcirculatory function in older men compared with young individuals. We measured NOx plasma concentrations and baseline and stimulated skin blood flow (SBF) by laser Doppler flowmetry in 39 male athletes [range, 22-72 years; maximal oxygen consumption (VO2max), 60.0 +/- 4.7 ml.min(-1).kg of body weight(-1) (mean +/- S.D.)] and 45 age- and sex-matched sedentary controls (VO2max, 38.0 +/- 7.1 ml.min(-1).kg of body weight(-1)). NOx concentrations were higher in athletes than in controls (50.4 +/- 16.3 compared with 39.0 +/- 15.4 micromol/l; P0.30, P<0.05). These findings show that chronic exercise may improve endothelial function in older (and young) men, probably by increasing NO availabilit