In 59 treated or untreated hypertensive subjects and 52 obese subjects (normotensive or hypertensive), intraarterial blood pressure (BP) was compared to simultaneous auscultatory measurements. In the hypertensive group, arm circumference was less than 35 cm compared to over 35 cm in the obese subjects. The occluding cuffs were 12 x 35 cm and 15 x 43 cm respectively. Mean difference between auscultatory and intraarterial systolic BP (SBP) was among the hypertensive -- 8.8 mm Hg (SDDIFF 9.0 mm Hg, range + 13/ - 28) and among the obese - 3.1 mm Hg (SDDIFF 13.8 mm Hg, range + 19/ - 49). Mean difference auscultatory-intraarterial diastolic BP (DBP) Phase V was among the hypertensive patients + 10.8 mm Hg (SDDIFF 6.8 mm Hg, range + 29/ - 8), and among the obese + 5.5 mm Hg (SDDIFF 7.3 mm Hg, range + 20/ - 10). Thus, a 15 x 43 cm cuff used in obese subjects with an arm circumference exceeding 35 cm gave quite as reliable measurements as a 12 x 35 cm cuff used in hypertensive subjects with "normal" dimension of the upper arm (less than 35 cm). It is emphasized that there is a wide scatter in the interindividual differences, and it is argued that a comparison between auscultatory and intraarterial BP should be performed in patients with poorly controlled hypertension.