To evaluate the age-related response of vasoactive factors during acute exercise, young (n = 8, aged 23.6+/-2 years) and old (n = 13, aged 77+/-6 years) healthy volunteers performed a stress test using a treadmill, and blood samples were taken before and after exercise. There were neither basal (old people 77+/-53 vs. young people 67.6+/-40 pg/ml) nor peak exercise-related (old people 77+/-43 vs. young people 66.8+/-34 pg/ml) differences in plasma adrenomedullin (AM) between both groups. AM did not increase with exercise in either group. Regarding plasma cAMP, there were neither basal nor exercise related differences, but this nucleotide increased with exercise in both groups (old people p < 0.0001, young people p < 0.05). Plasma Atrial Natriuretic Peptide (ANP) was higher in basal (116.3+/-64 vs. 46.8+/-21 pg/ml, p < 0.003) and after exercise samples (150.2+/-76.5 vs. 68.7+/-29.5 pg/ml, p < 0.004) in old people as compared with young people. Old people showed an increase in ANP with exercise (p < 0.05), but in young people, though there was a trend to increase, it did not reach statistical significance. There were neither basal nor exercise related differences in plasma cGMP, but this nucleotide increased with exercise in both groups. Angiotensin II (AT-II) levels were lower in basal and after exercise samples in old people as compared with young people. AT-II levels did not increase with exercise in either group. These data suggest that, with increasing age, the vascular tree develops resistance to ANP and higher sensitivity to AT-II, while AM levels do not change. Exercise makes ANP changes more evident, while AM and AT-II are not modified.