Two young adult monkeys (Macaca mullata) were trained to perform a delayed-response task that required the monkeys to remember a cued spatial position (left or right) over a delay interval and then to make a response to the cued position. Local injection of the alpha 2-adrenergic antagonist yohimbine (10 micrograms in 2 microliters saline) into the dorsolateral prefrontal cortex (Walker's area 46 and area 9) impaired the performance of the delayed-response task, and it was without effect on the performance of the task if there was no delay between the cue and choice signals. The main performing error after injection of yohimbine was that the monkeys responded to uncued position with higher rate. Local injection of the alpha 1-adrenergic antagonist prazosin (10 microgram in 2 microliters saline) or the beta-adrenergic antagonist propranolol (10 micrograms in 2 microliters saline) into the same cortical areas induced no significant effect on the performance of the task. The present study suggests that prefrontal alpha 2-adrenoceptors play an important role in the spatial working memory in young adult monkeys.