If there is a significant dichotomy between bilateral blood pressure determinations in both arms, it is often taken as a sign of some type of underlying pathology. We wished to evaluate what the normal variation might be for significant differences between blood pressures in both arms. Significant difference was arbitrarily chosen as a systolic blood pressure value greater than 10 mm Hg. Bilateral indirect blood pressure determinations were obtained in 100 subjects with no known history of hypertension in the sitting position. The blood pressure was obtained by 2 observers, one who recorded the systolic and diastolic blood pressure as announced by the person taking the blood pressures who was blinded to the actual values taken. The coefficient of variation in obtaining the blood pressures in each arm was determined in 5 of the 100 subjects. The age, sex, and handedness of each individual were recorded as demographic variables. The average left and right systolic blood pressures were 112.1 +/- 16.5 and 112.7 +/- 16.3 mm Hg, respectively. The average left and right diastolic pressures were 64.4 +/- 11.6 and 63.5 +/- 9.9 mm Hg, respectively. There was no significant difference between left minus right systolic or diastolic differences (Student's paired t-test). There were no significant differences in systolic or diastolic blood pressure between gender or between right and left handed individuals (non-paired t-test). The average coefficients of variation for right and left arm systolic blood pressures were 5.41% and 5.81%, respectively. Fifteen subjects had differences in systolic blood pressure between both arms exceeding 10 mm Hg (7% to 22%, 95% confidence interval). Differences of more than 10 mm Hg in indirect bilateral blood pressure recordings are frequent in normotensive individuals and probably do not per se indicate any abnormal pathology. In the right clinical situation, differences that are noted should probably be repeated and should be added to the total clinical picture when used to determine whether a pathologic condition is present.