Reduction of pressure on the lower part of the human body is believed to be capable of altering the normal fluid distribution. This could serve as a therapeutic method for emergency relief of the effects of hypertension, or it could be used as counterbalance for zero gravity and assist in preparing astronauts for reentry into the gravitational field. The present work describes a technique of assessment of the fluid shift caused by such pressure reduction. Thirty experiments were performed on four healthy subjects. The shift of fluid was assessed by measuring changes in body weight distribution of the tested subjects. The shift of fluid was assessed by measuring changes in body weight distribution of the tested subjects. The experimental results show that two processes may have taken place within the human body: shift of blood within the vascular system and diffusion of fluids from the circulatory system to the tissues. The total fluid shift ranges between 1 and 2 kg. It was proportional to the pressure gradient and exponential with time. The systolic blood pressure was reduced with the pressure reduction while the pulse rate increased.