The symptoms of panic disorder according to the diagnostic criteria DSM-III-R and MKN-10 are, except a few, virtually identical with those of latent tetany, defined in the tetanic questionnaire developed at the Department of Neurology of the University Hospital at Olomouc. The author formed a group of 20 patients treated in an psychiatric outpatient unit for panic disorder. These patients had examinations necessary for diagnosing latent tetany including clinical neurological examination, biochemical investigation with an emphasis on the levels of serum and red blood cell magnesium, and EMG. In a group of 20 patients treated for panic disorder, the author found a concomitant incidence of latent tetany with known etiology--decreased levels of intracellular magnesium--and causal treatment with magnesium salts in 18 (90%). As these nosological entities appear to occur concomitantly, the author recommends, in all patients treated for panic disorder, to examine the iontogram, red blood cell magnesium and EMG and, if the diagnosis of latent tetany is confirmed, to initiate therapy with magnesium salts whose long-term administration leads to remission of problems common to both nosological entities.