In order to assess the influence of a non-invasive test such as Duplex scanning on the management of patients with suspected carotid artery disease, we reviewed the data on all new referrals (n = 491) during a year. The patients were grouped according to the reason for the referral: 1, patients with focal neurological symptoms lasting less than 24 h (n = 156); 2, patients with focal neurological symptoms lasting longer than 24 h (n = 107); 3, patients with non-focal neurological symptoms (n = 147); 4, patients with asymptomatic bruits (n = 81). For all four groups there was a statistically significant relationship (chi 2; P less than 0 . 005) between the reporting of the presence of a high grade stenosis (more than 50 per cent diameter reduction) and the likelihood that the patient would undergo arteriography. The finding of a high grade stenosis on the arteriogram resulted in a greater number of patients undergoing carotid artery surgery. The results of this study indicate that the report of the non-invasive test influenced the decision-making process in the management of patients with suspected carotid artery disease.