It has been proven with clinical, psychological and electromyographic tests that the hyperventilation (HV) syndrome cannot be separated from so-called genuine tetany. Tetanic patients with and without HV are characterized by a significant hypocalcemia; but a significant hypomagnesemia is exclusively found in tetanic patients with HV attacks. Possible pathogenic mechanisms are discussed which may explain the HV attacks as a consequence of primary magnesium deficiency.