Based on a recently proposed reference range for plasma/serum Mg with its lower limit set at 0.76 mmol Mg/L the frequency of hypomagnesemia was evaluated in an unselected population group of about 16,000 individuals in total as well as in subgroups built according to sex, age and state of health. Hypomagnesemia was present in about 14.5 percent of all persons with generally higher frequencies in females and outpatients. In addition a slight but significant effect of age became overt. There was a continuous increase in the frequency of hypomagnesemia until the 29th year of life followed by a steady state. In elderlies, especially in old ladies, highest prevalence of up to one third of this subgroup occurred. Suboptimal levels were detected in 33.7 per cent of the population under study. These data clearly demonstrate that the Mg supply of the German population needs increased attention.