Changes in smooth pursuit eye movements and the P300 component of the auditory evoked potential were studied in patients with primary degenerative dementia during a double-blind, placebo-controlled study of ergoloid mesylates (Hydergine). After 18 weeks of treatment, P300 latency and amplitude, recorded at three scalp electrode sites, had not changed significantly. Smooth pursuit gain was elevated for the drug group under some stimulus conditions, suggesting a normalization of pursuit eye movement functioning. However, the results of several other measures of the quality of pursuit eye movements failed to corroborate this finding. (J Geriatr Psychiatry Neurol 1990; 3:41-47).