Apparant two binding sites, high and low affinity, were shown when Scatchard plotted after the rat brain membrane was analyzed for ³H-naloxone binding characteristics with opiate receptors. The maximum number of high binding sites (Bmax) was 8.79 fmol/㎎ brain membrane protein while the low affinity binding sites displayed the apparant dissociation equilibrium constant (Kd) of 9.09 nM. When the brain membrane was treated with phosphalipase A, Bmax has reduced to 7.13 fmol/㎎ and Kd to 0.32 nM. The changes in binding parameters with 1, 6, 12 weeks old rat brain were observed under various experimental conditions.