WITH the increasing interest in neurootology, the vestibular system is being tested more and more. Unfortunately, vestibular evaluation is far from satisfactory as yet, in spite of the continuous clinical and basic research being conducted. The attempt to elicit positional nystagmus is an integral part of vestibular testing, but with our present knowledge, interpretation of findings is unsatisfactory and drawing conclusions often difficult. By definition, a positional nystagmus (PN) is one that appears or changes in form or intensity after certain position changes of the head. The literature on it is rather confusing especially to the uninitiated in vestibular physiology. Nylen,1 in 1950, stated that a PN "must be considered to be one of the surest, most objective and most easily demonstrated signs of disturbance in the human vestibular system." Harrison,2 14 years later, voiced essentially the same opinion. Barber,3 in 1964, agreed with two reservations: vertical