The effects of diazepam and thiopental on voluntary saccades and pursuit eye movements were tested in 9 volunteers, with an interval of at least 2 weeks between tests. One, 4 and 8 h after intravenous injection of diazepam (0.3 mg/kg) or thiopental (6.0 mg/kg), voluntary saccades and pursuit eye movements were tested and blood samples taken for analysis of drug concentration. As compared to results of tests without drugs, a significant reduction both of saccadic peak velocity and gain of pursuit eye movements was found 1 h after injection of either drug, but not after 4 and 8 h. The amplitude of saccades elicited with the 60 degrees stimulus was significantly reduced 1 h after injection of diazepam. Latency of saccades increased significantly up to 4 h after injection of either drug. No significant correlation was found between peak velocity of saccades and blood concentration of either thiopental or diazepam 1 h after administration. The present results confirm that in man saccades and pursuit eye movements are reduced by benzodiazepines and barbiturates, but provide no support for the previously described efficacy of saccades in monitoring the effect of benzodiazepines. It is hypothesized that diazepam and thiopental also induce reduction of voluntary saccades and pursuit eye movements via a general sedation of the central nervous system (CNS), besides having specific effects on CNS structures important to the performance of voluntary eye movements.