AbstractClonidine (0.03–0.06 mg/kg), in a dose‐ and delay‐dependent manner impaired the ability of aged rhesus monkeys to perform a microcomputer‐controlled delayed response test similar to that used previously by Bartus et al. (J. Gerontol.33:858–871, 1978). These doses of clonidine produced overt sedation, increased response latencies and decreased the percentage of correct responses. Continued disruption of delayed response performance was seen during 11 days of repeated daily clonidine (0.04 mg/kg) administration. Performance immediately returned to preexisting baseline levels on the day following cessation of this repeated drug regimen. In addition, repeated clonidine administration did not alter responsivity to acutely administered clonidine, suggesting that tolerance did not develop rapidly to the disruptive effects of this agent. These data indicate that clonidine impairs delayed response performance in aged rhesus monkeys under these testing c