We reportin vivoandin vitroantagonist binding characteristics of the naturally occurring Ser311→Cys variant of the human D2dopamine receptor. Striatal receptor binding characteristicsin vivowere measured with positron emission tomography and the D2antagonist [11C]raclopride. Thein vitroaffinity of raclopride for the Ser311→Cys variant and the wild type receptor was studied in membrane binding assays from stably transfected cell lines. One healthy male carrying the heterozygous Ser311→Cys (TCC→TGC) substitution was identified with denaturing gradient gel electrophoresis and DNA sequencing. The striatal D2receptor binding characteristicsin vivoin this subject were normal. This was supported by thein vitrodata as the Ki values of raclopride for the Ser311→Cys variant and the wild type receptor were identical. Our data suggest that the Ser311→Cys variant of the human D2receptor does not influence antagonist-receptor recognitionin vivoorin vitro.