Eye movement abnormalities were quantitatively assessed in four patients with clinically pure cerebellar atrophy (group A), six patients with brainstem plus cerebellar atrophy (group B), and five patients with Friedreich's ataxia (group C). Twelve patients had one or more types of spontaneous nystagmus: eight gaze nystagmus, three rebound nystagmus, two positional nystagmus, and one vestibular nystagmus. Caloric-induced and rotatory-induced nystagmus was hyperactive in group A and diminished in group C. Group B had mixed responses. All patients demonstrated significant fixation instability and impaired smooth pursuit. There was dysmetria of voluntary saccades, with flutter and "rebound" saccades. Nine of 15 patients had significant slowing of induced saccades, including two patients in group A. It is concluded that quantitative vestibulo-ocular tests can be useful in classifying the cerebellar atrophy syndromes.