The effects of the new 5-HT3 receptor antagonist, DAU 6215, on aged rats' cognition were assessed in the Morris water maze task. Task performance of aged animals that received acutely the dose of 10 micrograms/kg IP was not different than that of their aged controls treated with the vehicle. Conversely, a repeated IP administration of 10 micrograms/kg DAU 6215 for 3 weeks significantly improved task performance of the aged animals as compared to that displayed by the old rats treated with the vehicle.