The active enantiomer R-SKF 82957 was labeled with 11 C by N-[ 11 C]methylation of the full dopamine (D 1 ) agonist R-SKF 81297, using [ 11 C]methyl iodide in the presence of N-ethyldiisopropylamine, in high specific activity, radiochemical purity and yields. Compared with the D 1 agonist R/S-[ 11 C]SKF 82957, R-[ 11 C]SKF 82957 showed higher binding in the D 1 rich regions, such as striatum and olfactory tubercles (∼1.7 times), thereby improving the tissue contrast. R-[ 11 C]SKF 82957 exhibited high in vivo binding selectivity for D 1 receptors in rats, because only high doses of D 1 competitors, but not D 2 or serotonin (5-HT 2 ) blockers, significantly reduced the radioactivity levels in all brain areas. No labeled metabolites were detected in rat brain. These results indicate that R-[ 11 C]SKF 82957 will provide more sensitive measurements of D 1 receptors in in vivo studies than the racemic mixture.