We studied, by dietary recall, the calcium and magnesium intake in 1109 adolescents aged 14-18 years; from 128 we collected a 24-h urine sample to determine electrolyte excretion. Subjects with blood pressure greater than 90th percentile (211) did not consume less calcium or magnesium than those with blood pressure less than 50th (597). Urinary calcium excretion tended to be higher in the adolescents with the highest blood pressure, the difference being statistically significant in males. Urinary sodium excretion also tended to be higher in those adolescents with blood pressure above the 90th percentile than in those with blood pressure below the 50th percentile, the differences being statistically significant in females. A positive significant correlation was found between systolic blood pressure and both calcium and sodium excretion. Our results suggest that hypercalciuria is present in the early phase of hypertension and demonstrate that adolescents at high risk of developing hypertension consume the same amounts of calcium and magnesium as those with low blood pressure.