Sixty five women were in the third trimester of pregnancy (29-40 weeks of gestation) submitted to the study including 35 with primary hypertension (the studied group) and 30 healthy (control group). The following parameters were measured in blood serum and urine from 24 hrs, collection: total Ca and Ca++, inorganic phosphorus (Pi) and magnesium. Generally accepted micromethods were used; Ca++ was measured using AVL type 9140 analyser. Women of the studied group presented mean blood pressure 164 +/- 14/106 +/- 9.7 mm Hg and did not have proteinuria and oedema. They presented decreased concentrations of total Ca (p < 0.004) and ionised Ca++ (p < 0.004), and an increase of Pi (p < 0.002) in blood serum. No differences in magnesium concentrations were found. Distinct decrease of calcium excretion in urine was found in hypertensive women (4.50 +/- 2.76 vs 6.60 +/- 3.4 mmol/24 hrs, p < 0.024). No alterations in phosphorus and magnesium urine excretion were observed in women with hypertension (women of both groups had the same volume of 24 urine). Our study concludes the main alterations in calcium-phosphorus-magnesium homeostasis in pregnant women with primary hypertension are the calcium homeostasis alterations. Phosphorus homeostasis is less affected while magnesium distribution does not change. Hypocalciuria might be related to impaired glomerular filtration in this pathology in pregnancy. Hypocalciuria and lowered serum concentrations of total Ca and ionised Ca++ might prove general deficiency of this element in pregnancy complicated by primary hypertension.