The optically active compound, R (-)-5-[2-[[2-(2-ethoxyphenoxy)ethyl]amino]propyl]-2-hydroxybenzenesulfona- mide in good optical purity, a metabolite of the .alpha..sub.1-adrenergic blocking agent tamsulosin, and methods for the preparation thereof. Pharmaceutical compositions including the optically active compound and methods of treatment comprising administration of an effective .alpha..sub.1-adrenergic antagonistic amount of such compositions to mammals.