The accuracy of 4 different ambulatory blood pressure (BP) monitors was assessed by comparing them to simultaneous intraarterial BP (contralateral brachial artery) during rest, isometric and dynamic (bicycle) exercise in 48 hypertensive patients undergoing invasive hemodynamic evaluation. The differences between the intraarterially determined BP and values obtained by the various monitors were then compared to differences between BP measured directly and by 2 clinicians using a standard mercury column in 10 additional hypertensive patients. The monitors studied were the Accutracker II (auscultatory with mandatory electrocardiographic gating), Colin ABPM 630 (auscultatory or oscillometric), Del Mar Pressurometer IV (auscultatory with optional electrocardiographic gating) and SpaceLabs 90202 (oscillometric). During rest, the differences between intraarterially and clinician-determined systolic and diastolic BP were 4 +/- 8 and -4 +/- 6 mm Hg, respectively. The Accutracker II and Colin ABPM 630 using the auscultatory method showed less disparity and closer limits of agreement (2 standard deviations of the mean difference) with intraarterial BP than the clinicians' measurements, whereas the other units showed similar or greater limits of agreement. During both isometric and dynamic exercise, mean BP differences between intraarterial and clinician determinations were similar to those at rest but the limits of agreement increased. The limits of agreement between intraarterial and monitor-derived BP also increased during exercise compared to differences observed at rest. The Accutracker II and Colin ABPM 630 using the auscultatory method had limits of agreement with intraarterial BP that were either similar to or less than the clinician's, whereas the Colin monitor using the oscillometric method and the Del Mar Pressurometer IV showed greater disparity.(ABSTRACT TRUNCATED AT 250 WORDS)