The origin of high blood pressure is still not clear. Measuring the blood pressure does not give sufficient information concerning the disturbance in its regulating mechanism, which apparently results in some instances from functional changes. Repeated measurements during the day and early in the morning are of greater value, but do not yield further insight into the mechanism of hypertonic disturbances. In recent studies1 of presenile disturbances of blood pressure I described some new tests which, in my opinion, aid in determining the disturbances in the regulating mechanism in high blood pressure. By means of these tests, one can demonstrate the compensating power of the organs which regulate blood pressure level. The curves obtained in my labor test illustrate the regulating action of these organs, vasomotor center, vasomotor nerves, etc., which are independent of the otherwise variable blood pressure level. The labor test is performed as follows: The blood pressure