The authors take into account two different types of stationary, persistent and direction-changing nystagmus (ny): 1) the horizontal bidirectional ny (nyOB), apogeotropic (nyOBA) and geotropic (nyOBG); 2) the tridirectional apogeotropic ny (nyAT). The nyOBA was identified in experimental studies in 1973 but no other studies on the subject have been published since then. In existing literature the nyOBG has been reported in only one paper, whereas the nyAT has not yet been studied at all. The nyOBA is the combination of a 2nd degree left ny with the head turned right and a 2nd degree right ny with the head turned left. The nyOBG is the combination of a 2nd degree right ny with the head turned right and a 2nd degree left ny with the head turned left. The nyAT is a 2nd degree apogeotropic ny noticeable with the head turned left, right and in the position of Rose (head hanging down). From among a total of 5,960 consecutive vestibular examinations performed from 1986 to 1990, the authors chose those presenting nyOBA, nyOBG and nyAT and discuss them in the light of other vestibular findings and clinical diagnosis. A routine vestibular examination aims at verifying an eventual, spontaneous/evoked ny with the head turned right and left, in the position of Rose and in the two rapid Hallpike positionings. Frenzel glasses are used for detecting the gaze and rebound ny and these, in turn, are checked for visual fixation. During the caloric stimulation, according to the Fitzgerald-Hallpike method, the ny visual suppression test is performed at the culmination period. When electronystagmography is performed, visual oculomotor reflexes are often tested as well. The nyOB and/or nyAT were observed in 3.9% of the patients (234 subjects). The nyOB was present in 177 patients as follows: apogeotropic ny in 128 and geotropic in 49. This was the only vestibular finding in 46.9% of the nyOB cases (83 out of 177 patients). The nyAT was observed in 57 patients and in 17.6% of them was the only pathological finding of the otoneurological examination. When nyOB or nyAT were observed, clinical diagnosis evidenced their central origin in 138 of the 234 patients, most frequently present in cranial trauma, vertebral-basilar vasculopathy and multiple sclerosis. In a limited number of cases some sign of peripheral vestibulopathy were also observed.(ABSTRACT TRUNCATED AT 400 WORDS)