The supracallosal bundle (SCB) and prefrontal cortex (PFC) receive projection from medial forbrain bundle (MFB) of the lateral hypothalamus (LH) in relation to reward system. The major purpose of the present study was to compare the intracranial self-stimulation (ICSS) rate of both the SCB and PFC with special emphasis on its associated behavior. The results obtained were as follows: 1) self-stimulation was obtained with electrodes historogically varified as being in the SCB (16 of 23 electrodes positive for ICSS) and the medial PFC (3 of 16 electrodes positive for ICSS). Electrodes dorsal and far lateral to the SCB and PFC were mainly negative (see Fig. 1). 2) Rats with SCB or PFC electrodes, chiefly showed a rearing associated with its ICSS. When stimulation electrodes were more posterior or lateral sites in the SCB and PFC, clonic movements of forelimb and head were occasionally observed (Fig. 1). 3) For neuron in the LH, stimulation of the SCB via chronic electrodes positive for ICSS produced two characteristic types, i.e. postinhibitory rebound type (Fig. 2A) and driven inhibitory type (Fig. 2B-1). It was suggested that fibers of MFB were activated by stimulating SCB-ICSS sites.