Regional cerebral blood flow (rCBF) was measured by the xenon-133 inhalation method in an unselected group of nine chronic hemodialysis patients before and after a single hemodialytic treatment. All patients underwent neurological, neuropsychological, and biochemical evaluations on the same occasions. Predialysis rCBF values did not differ from those obtained in age-matched normal controls. Following hemodialysis, there was a mild reduction in the rCBF by a mean of 7 +/- 2.6% (p = 0.02). The posthemodialysis rCBF reduction was not associated with any neurological or cognitive dysfunction. The causes of hemodialysis-induced rCBF decreases are unknown, but increased blood viscosity and biochemical changes, such as urea reduction and blood alkalinization, may play a role.