The influence of dopamine and its antagonists on neuronal activity related to the delay period of a delayed response task was examined in the monkey prefrontal cortex. Iontophoretically applied dopamine enhanced the delay-related neuronal activity, while fluphenazine and haloperidol attenuated the activity. Sulpiride had no effect on the activity. The results suggest that dopamine promotes processing of spatial short-term memory by increasing memory-related activity in the primate prefrontal cortex, probably via D1-type dopamine receptor.