Age-related alterations in cerebral vascular function may be better understood by investigating cerebral response to exercise. We performed a MR study involving low/moderate intensity exercise in healthy young and older subjects. We assess the effect of exercise on CBF response, cerebral oxygenation, and CMRO2. We also investigate the relationship of GM-volume and physical fitness with ageing. At rest, there was no difference between CBF and CMRO2 but an increase in oxygen extraction with age. On exercise the age-related increase in OEF remained, however CBF and CMRO2 were blunted in older subjects. GM-volume was found to be associated with VO2max.