['Validation procedures of automated blood pressure measuring devices are carried out at rest only.', 'We aimed to determine whether venous blood redistribution affects the accuracy of the OMRON HEM-705CP (Osc). Lower body negative pressure stimulus (-40 mmHg) (LBNP) was used to simulate changes of body position.', 'Fifty-four young healthy volunteers had their blood pressure (BP) measured simultaneously by Osc and mercury sphygmomanometer (HgS) at rest (at 3 and 5 min) and during LBNP (at 7 and 9 min).', 'Differences (delta) between HgS and Osc for systolic and diastolic BP (SBP and DBP) were calculated. The deltaSBP obtained in minute 9 (deltaSBP-9) was bigger than the one taken in minute 5(deltaSBP-5) (-2.89+/- 4.3 versus -1.35+/-5.2 mmHg, P<0.02). The rest of the deltaSBP values and all the deltaDBP values were constant at rest and during venous blood redistribution caused by LBNP. We calculated the fall in SBP separately for HgS and Osc by subtracting SBP-9 from SBP-5 for each patient. The fall measured by Osc was bigger than by HgS (-5.87+/-4.0 versus -4.3+/-4.5 mmHg; P<0.02). When graded according to British Hypertension Society protocol, Osc remained in the class of recommendation (A or B) for every minute of the procedure.'] Does venous blood redistribution alter the accuracy of Omron HEM-705CP?