Abrupt increases in electrical activity can be recorded from the medial basal hypothalamus of the rhesus monkey and these bursts are correlated with a pulse of LH release from the anterior pituitary. In this study we have localized the tips of the electrodes from which such electrical activity can be recorded and have attempted to correlate the placement with the presence of immunoreactive LHRH neurons and axons. Electrodes associated with bursting activity were found as far rostral as the suprachiasmatic nucleus and as far caudal as the premammillary nuclei. The majority were found in the medial basal hypothalamus including the region of the arcuate nucleus, the retrochiasmatic zone and the dorsal aspect of the median eminence. The tips of the electrodes were associated with either LHRH neurons or axon bundles. Negative electrodes (those not associated with bursting electrical activity) which did not exit through the ventral surface of the brain nor enter the ventricle were found in the same regions of the hypothalamus as positive electrodes. Although it is tempting to associate the bursting electrical activity with the LHRH neurosecretory system, such a correlation cannot yet be made.