Is humeral blood pressure identical in the right arm and left arm? We attempted to answer this question by simultaneous measurement of pressure on each side by a semi-automatic indirect method. Results were analysed by the linear regressions method. This study showed that it is possible to estimate the pressure on one side on the basis of a measurement made on the opposite side. The accuracy of this estimation is +/- 10 mmHg regarding the blood pressure of a given individual and is +/- 4 mmHg in terms of the mean blood pressure of the population in general. Thus, provided there is no anatomical abnormality of the arterial system, it would seem to make no difference if blood pressure is measured on the left side or right side.