The cingulate cortex, especially its anterior portion has been found to be connected with the head of the caudate nucleus in our previous study. In order to ensure accurate placement of adequate amounts of HRP in the cingulate cortex, a microiontophoretic delivery technique coupled with single cell recording was employed. The use of electrophysiological criteria as aids in placing the injection is described in detail. It was found that the influence of the caudate neuron was inhibitory, and the cingulate neurons responded with monosynaptic IPSPs to caudate neuron stimulation. Following HRP injections into the cingulate cortex, the retrogradely labeled cells were found in the head of the caudate nucleus. It is obvious that some neurons of the head of caudate nucleus which have inhibitory effect on unit discharge of the cingulate cortex project to the anterior portion of the cingular cortex.