In order to evaluate olfactory vertigo a new equilibrium test termed equilibrium test for olfactory vertigo has been devised. In this test, a subject is asked to inhale the vapor of liquid garlic odor through the nostrils for 60 seconds at a natural respiration rate. Ten minutes after the completion of inhalation the subject is examined using various equilibrium tests, such as drift reactions of the upper and lower limbs, the test for spontaneous nystagmus and that for eye tracking. Ten normal subjects and 35 patients with cranio-cervical injury were examined using this new equilibrium test. The results obtained were as follows:<br>(1) In normal subjects neither vertigo nor ataxia was induced when this test was carried out.<br>(2) In traumatized patients the appearance and/or increase of vertigo and ataxia were observed with the following results:<br>i) The test was positive in patients who complained of hyperosmia and experienced vertigo due to olfaction.<br>ii) Patients with a positive test for olfactory vertigo showed hypersensitivity to adrenaline and the appearance and/or increase of ataxia resulted when this drug was administered. Furthermore, there was a tendency that the pattern of ataxia induced by garlic was similar to those induced by adrenaline.<br>iii) There was a tendency that the pattern of ataxia due to olfaction was specifically correlated with the locus of lesions in the equilibrium system.<br>iv) A positive sign of the test for olfactory vertigo was more marked in patients with cerebellar ataxia than in those without. Furthermore, in patients with cerebellar ataxia this tendency became more evident in accord with the severity of the ataxia.<br>v) Olfactory vertigo was not always accompanied by vertigo of psychosomatic origin, although there was a tendency that patients who showed the latter type of vertigo developed the former type.<br>vi) Cloxazolam, a minor tranquilizer, which belongs to the Benzodiazepine group, was found helpful in relieving vertigo due to olfaction. However, no beneficial effect was produced in patients who showed both olfactory vertigo and cerebellar dysfunction.<br>With reference to the above results and those from our previously reported animal experiments, the following conclusions were drawn:<br>(1) Olfactory vertigo is closely concerned with over-excitement of adrenergic components, particularly those involved in the limbic system, hypothalamus and brain stem.<br>(2) The cerebellum is not a primary neural element in the production of olfactory vertigo. However, it probably contributes to the enhancement of vertigo of this type, affecting the activity of the primary neural elements described in (1).<br>(3) The neural mechanism of olfactory vertigo differs from that of psychosomatic origin, although there are some common neural elements between the two.<br>(4) Procedures which inhibit over-excitement of adrenergic components in the central nervous system are helpful in relieving the vertigo and disequilibrium due to olfaction.