Characteristics of [3H]- Sulpiride binding in rat striatal membranes by ligand binding assay were analyzed. The results showed that the binding is specific

saturable

reversible and selective. Scatchard analysis of the data revealed a single binding component with a dissociation constant （Kd） of 5.17±1.13nmol/l （X±SD

n = 5） and a maximum binding capacity （Bmax） of 917.0±133.2fmol/mg protein （X±SD

n = 5）. Based on the ligand binding assay

[3H]- Sulpiride radioligand assay has been developed. The linear range of the assay was 1-100nmol/l. The sensitivity was 49.25pg/ml. The coefficients of intra- and interassay variation were 3.35% （n = 10） and 10.6% （re = 4）

respectively.