Study hypothesis: supplementary magnesium may influence the blood calcium level in treated hypoparathyroid patients. Patients will be treated with supplementary magnesium (350 mg/day) for 3 weeks. Calcium and other relevant blood parameters will be measured before the treatment, at the end of treatment and 2 weeks after stopping treatment.

Inclusion Criteria:

• primary or secondary hypoparathyroidism
• treatment with calcium plus vitamin D analogue
• ionized calcium 1,0-1,29 mmol/L
• magnesium level 0,7-1,05 mmol/L
• TSH 0.1- 10 imU/L

Exclusion Criteria:

• any other disease known to influence plasma Ca level
• pregnancy
• creatinine > 150 microM/L
• patient has used supplementary magnesium within 2 previous months