I read with great interest a recent commentary by Moser1 published in the August 8, 1994, issue of the ARCHIVES, in which he discusses ambulatory blood pressure monitoring as a possible strategy in containing cost of care while maintaining quality of care in the management of hypertension.1 Moser states that "approximately 15% to 20% of the recordings are unreadable or unusable." This estimate is too high. Our institution has a quality control program that separately reviews in detail a randomly selected 15% of all 24-hour ambulatory blood pressure studies done for clinical purposes. All these studies are begun with careful validation and detailed instructions to the patient, eg, to hold the arm still and to stop activities when inflation of the cuff begins. For the calendar years 1991 through 1993, 114 of the studies were reviewed for quality control. A total of 17 988 blood pressure measurements were