The effects of haloperidol on the electroretinogram were studied in mice injected intraperitoneally with haloperidol. A dose-related study was performed. A significant decrease in the amplitude of the b-wave was found in the mice injected with more than 20 mg/kg of haloperidol. However, the peak latency of the b-wave and the stimulus intensity required to elicit a b-wave of one half of the maximum b-wave amplitude remained unchanged. No significant changes were found in the a-wave. This change in the electroretinogram recovered 24 hours after the injection. These results suggest that functional change occurred at the retinal level after intraperitoneal injection of haloperidol.