Using instrumental neutron activation analysis, the variations in the serum levels of Br, Cs, Na, Rb, Se, and Zn were investigated
in 18 persons in the normal state. By determining the element levels in relation to changes is the serum water content, information
about the binding to the serum protein was obtained. The influence of physiological factors on the serum element levels was
investigated. Changes in the concentrations due to variations in the protein/water ratio and in the zinc level as a result
of different posture were observed. When standardized sampling procedures were used, the variations in the serum element concentrations
during one hour and from day were found to be less than 10%.