Using multibarreled glass micropipettes, we recorded single-unit activity in the putamen, and iontopho retically applied D1 and D2 dopamine receptor agonists (SKF38393, quinpirole) and antagonists (SCH23390, sulpiride) while two monkeys were performing a delayed Go/Nogo task. The putaminal neurons exhibited changes in activity during various task periods (hold, cue, delay, response, and reward periods) in both Go and Nogo trials. Of 296 task-related putaminal neurons, 87 showed activity changes in Go trials only (Go type), 74 in Nogo trials only (Nogo type), 99 in both trials during the same task periods (Both type), and 36 in both trials but during different task periods (Different type). These 296 neurons were examined as regards the effects of both D1 and D2 agonists and/or antagonists, and 234 neurons responded to either D1 - or D2-related substances or both. Among them 41% of neurons responded to the D1 substances only (D1 group), 36% responded to the D2 substances only (D2 group), and 23% responded to both D1 and D2 substances (D1D2 group). During the iontophoretic application of the D1 and D2 substances, most of the responding neurons changed their task-related activity but not their baseline firing rates. The D1 agonist increased the activity in 19 neurons and decreased it in 105 neurons. On the other hand, the D2 agonist increased the activity in 54 neurons and decreased it in 50 neurons. The D1 and D2 substances modulated the activity in both Go and Nogo trials. Each of the three D1/D2 groups (D1, D2, and D1D2 groups) contained all four Go/Nogo types (Go, Nogo, Both, and Different types) of neurons. Percentages of each Go/Nogo type of neuron were comparable among the three D1/D2 groups. The D1 and D2 substances modulated the activity related to various task periods. Each of the three D1/D2 groups included neurons activated during the cue, delay, response, or reward period in Go and Nogo trials. Distributions of the neurons related to each task period were similar among the D1/D2 groups. These results suggest that dopamine can modulate the activity of single putaminal neurons through both D1 and D2 receptors and that the dopaminergic modulation through the two receptors in the putamen affects similar types of signals in behavioral control.