We compared the usefulness of two methods for diagnosing asymptomatic brain infarction: an ultrasonic quantitative flow measurement system (QFM) and a transcranial Doppler arteriography (TCDA). A total of 137 patients (73 men and 64 women) who underwent magnetic resonance imaging of the brain, QFM, and TCDA were enrolled. Their ages ranged from 41 to 83 years (mean age, 63 years). The patients were divided into 3 groups: 45 without cerebrovascular disease (Group N); 40 with asymptomatic brain infarction (Group AS); and 52 with lacunar infarction (Group LI). The mean blood flow in the common carotid artery (CCA-BF) was measured by QFM. The mean blood velocity and Fourier pulsatility index in the middle cerebral artery (MCA-BV, MCA-PI) were measured by TCDA. In Group N, 28 patients were examined twice at a mean interval of 2 years; 19 remained without asymptomatic brain infarction (Group N1), and asymptomatic brain infarction developed in the remaining 9 (Group N2). The 3 groups differed significantly in MCA-PI (N < AS < LI), but not in CCA-BF or in MCA-BV. The MCA-PI in Group N2 was higher than that in Group N1. These results indicate that the Fourier pulsatility index determined by TCDA may be useful for detecting the onset of asymptomatic brain infarction.