In developed countries, the recommended dietary amounts of magnesium have been set at 6 mg/kg day. The magnesium requirements for optimal health in the adult population depend on mesological and constitutional conditioning factors. They may intervene at every stage of magnesium metabolism: absorption, circulation, storage and excretion. The influence of other nutrients is more significant on magnesium absorption than on urinary excretion. Among the multiple interactions it is important to emphasize the maintenance of a Ca/Mg ratio close to 2 in the intake. Magnesium deficit and stress reinforce each other in a pathogenic vicious circle. The Bw35 allele of HLA typing and behavioural type A discriminate two constitutional factors increasing magnesium requirements. The effective passive regulatory mechanism for magnesium overload, the lability of the active regulatory mechanisms for magnesium deficit and the considerable need for exchangeable magnesium are factors which attribute special importance to balance studies in determining the magnesium intake which prevents negative magnesium balance and magnesium deficiency. Marginal primary magnesium deficit affects a large proportion of the population (15 to 20%), in keeping with a daily mean magnesium intake slightly over 4 mg/kg day versus the Mg RDA of 6 mg/kg day. A physiological oral magnesium load test, evaluated through non-specific and specific clinical and paraclinical items, constitutes the best proof that the clinical pattern depends on an insufficient magnesium intake, confirmed after one month of supplementation. Further research appears necessary.(ABSTRACT TRUNCATED AT 250 WORDS)