Changes in smooth pursuit eye tracking of horizontal sinusoidal target movement before and after up to 10 mg oral diazepam were measured electrooculographically in diazepam-naive humans. Diazepam produced a dose-dependent reduction in gain of pursuit eye movements at target frequencies of 0.4–1.6 Hz. Cross-correlation of eye and track was significantly reduced at most frequencies showing gain reduction after 10 mg diazepam. Eye-target phase relationship was not systematically altered by drug. Visual inspection of smooth pursuit tracking records showed reduced peak-to-peak amplitude of eye tracking along with replacement of smooth pursuit with saccadic pursuit, especially after 10 mg. Changes in smooth pursuit eye tracking after diazepam were similar to those changes reported in the literature associated with olivopontocerebellar atrophy and were quite unlike the changes in smooth pursuit after opiates, as previously reported. The role of cerebellar benzodiazepine binding sites in diazepam disruption of eye tracking was discussed.