The total concentration (

R

T

) and equilibrium dissociation constant (

K

D

) of DA-3 dopaminergic receptor in rat striatum were investigated by

3

H-dopamine binding assay

and the concentration of antagonist producing a half-maximal inhibition (

IC

50

) and dissociation constant of the receptor-antagonist interaction (

K

i

) of apomorphine and some classical antipsychotic drugs were measured by competitive binding of labelled and unlabelled ligands. The results showed that: 1.

3

H-dopamine binding sites have some essential characteristics of receptor; 2. apomorphine behaves like a mixed agonist-antagonist; 3. the action of classical antipsychotic drugs is not related to DA-3 dopaminergic receptor.