The authors examined the efficacy of a 1-MHz transducer in routine ultrasound monitoring. Fifty outpatients (34 women, 16 men; mean age, 65 +/- 2) with inadequate temporal bone window for examination with 2-MHz transducers were re-examined with a 1-MHz transducer. Additionally, 50 controls (34 men, 16 women; mean age 49 +/- 2) with adequate temporal bone window were examined with both the 1- and 2-MHz transducers. Signal quality was classified as good (GQ), adequate (AQ), or poor (PQ). Finally, 30 normal controls were examined with both transducers under standardized conditions, to evaluate potential differences in velocity measurements. A total of 90 temporal windows were lacking in the 50 patients. Use of the 1-MHz transducer resulted in identification of the middle cerebral artery in 68 cases (76%; PQ, n = 13; AQ, n = 29; GQ, n = 26), the anterior cerebral artery in 51 cases (57%; PQ, n = 23; AQ, n = 17; GQ, n = 11) and the posterior cerebral artery in 46 cases (51%; PQ, n = 12; AQ, n = 21; GQ, n = 13). Examination was feasible with both transducers in the 50 controls, with minimal differences in signal quality between the two transducers. Correlation between velocity values acquired with the 1- and 2-MHz transducers was significant for all vessels examined. Best values were measured for the middle cerebral artery, followed by the anterior cerebral artery and posterior cerebral artery. The authors conclude that the use of the 1-MHz transducer increases the yield of transcranial Doppler sonography.