Two groups of subjects, matched for age, were studied. The first group consisted of 190 healthy subjects, the second, of 60 patients with vertebrobasilar transient ischemic attacks (TIAs), 22 of whom underwent angiography. After it was ascertained that the findings from continuous-wave (cw) Doppler of carotid and vertebral arteries, performed in the standard position, were normal, the examination was then done in De Kleyn's position, the velocity signal being detected at the mastoidal slopes. The abnormal findings were classified into two groups: "loss of diastolic velocity signal" and "absence of velocity signal." In the control group, changes of flow were detected in 6.31%, whereas in the group of patients abnormal Doppler parameters were detected in 33.33%. None of the patients who were submitted to angiography showed abnormal hemodynamic findings. The authors suggest that the detection of the velocity signal of the vertebral arteries in De Kleyn's position could be of help in revealing conditions that could cause, in time, signs and/or symptoms of vertebrobasilar insufficiency in subjects with possible asymptomatic anomalies of the circle of Willis.