In 32 patients with asymptomatic white matter lesions (WMLs), we evaluated the age-related changes in the number of white matter lesions, cerebral blood flow (CBF), cerebrovascular resistance (CVR) and mean arterial blood pressure (MABP). CBF was measured with the intravenous 133Xe injection method. The number of WMLs in whole brain was measured by the magnetic resonance imaging. CBF decreased with advancing age (r = 0.529; p less than 0.01), while the number of WMLs (r = 0.39; p less than 0.05), CVR (r = 0.464; p less than 0.01) and MABP (r = 0.229; ns) increased with advancing age. There was a significantly negative correlation (r = -0.499; p less than 0.01) between CBF and the number of WMLs. While, CVR showed a positive correlation with the number of WMLs (r = 0.468; p less than 0.01). Multivariate regression analysis with stepwise forward selection method indicated that the number of WMLs and age were independent and negative predictors for CBF, while other factors did not. CBF decreased with a concomitant rise in CVR. On the basis of the results listed above, we assumed that ischemic damage of the white matter and/or functional suppression of distant loci due to the primary tissue damage are the best explanation for CBF reduction in asymptomatic individuals with WMLs. High resolution CBF imaging as well as evaluation of structural alterations in cerebrovascular vessels should be required to further define the mechanisms.