We observed the urinary calcium in 103 patients in the third trimester of pregnancy and the relation between the 24 hour calcium excretion and the calcium/creatinine ratio of a single void urine sample. The study population included 75 normal pregnant women and 28 pregnant woman with pregnant hypertension syndrome. The 24 hour urinary calcium excretion in the patients with pregnant hypertension syndrome was significantly lower (0.70 +/- 0.36 mmol/L) than that in normal pregnant women (4.00 +/- 1.90 mml/L) P < 0.0005. The 24 hour calcium excretion correlated well with the calcium to creatinine ratio of a single void morning urine sample in the two groups. We conclude that the urinary calcium excretion can be used as an indicator for pregnant hypertension syndrome. The 24 hour urinary calcium excretion can be estimated from a single void urine sample. Pregnant hypertension syndrome is associated with hypocalciuria, probably due to increased tubular reabsorption of calcium.