The intention of this study was to examine the relation of clinical variables and cognitive dysfunction to cerebrovascular blood flow in a sample of patients with Alzheimer's disease without any sign or symptom of cardiovascular or cerebrovascular disease. The patients met DSM-III-R criteria for dementia of Alzheimer type. Blood flow velocities in the anterior, middle (MCA) and posterior cerebral arteries were recorded using transcranial Doppler sonography. Several psychometric tests including the Mini-Mental State Examination (MMSE) were performed. The patients' age correlated significantly with the systolic flow velocity in the left MCA (r = -0.57) explaining 24% of the total variance; there was a reduction of the mean flow velocity of 0.7 +/- 0.2 mm/s for every additional year. The MMSE correlated significantly with the systolic flow velocity in the left MCA (r = 0.62) explaining 29% of the total variance. The correlations of flow velocities with age indicate that even in very old patients there is a progressive reduction of cerebral blood flow velocities. The independent negative correlations of flow velocities with cognitive dysfunction indicate that there are progressive cerebrovascular flow reductions in the course of Alzheimer's disease. Both facts should be taken into account when Alzheimer patients are compared with other samples.