(+/-)-2-(5,6-Dimethoxy-1,2,3,4-tetrahydro-1-naphthyl)imidazoline has been resolved into its (+) and (-) enantiomers, and the absolute configuration was established by single-crystal X-ray diffraction studies. The more active isomer has been assigned the R absolute configuration. Cleavage of the respective (+)- and (-)-dimethyl ethers with boron tribromide provided the corresponding (+)- and (-)-2-(5,6-dihydroxy-1,2,3,4-tetrahydro-1-naphthl)imidazoline hydrobromides and these were pharmacologically characterized. In various preparations, the R enantiomer has been shown to be an extremely potent alpha agonist with preferential activity at the alpha 2-adrenergic receptor.