Benign paroxysmal vertigo (BPV) is a clinical syndrome of vestibular origin although generally no evidence of vestibular dysfunction can be demonstrated with conventional tests. In a review of 1350 consecutive dizzy patients, there were 125 with BPV and of these, 33 underwent a quantitative rotational test of vestibular function. The rotational results showed reduces vestibular system gain for these BPV patients. In addition, they could be subdivided on the basis of a normal or shorter cupular time constant (Tc). Separation of patients into diagnostic categories revealed that those categorized as cupulolithiasis and viral labyrinthitis had a normal Tc range and those categorized as trauma and idiopathic had a short Tc. The reduced gain and short Tc in the latter group suggest hair cell and/or nerve damage since these same changes occur in patients with destructive peripheral vestibular disease.