This invention is directed generally to zilpaterol enantiomer compositions, and, in particular, to compositions comprising the 6R, 7R zilpaterol enantiomer in an amount that is greater than that of any other enantiomer. This invention is also directed to processes for making such compositions; methods for using such compositions to, for example, increase the rate of weight gain, improve feed efficiency, and/or increase carcass leanness in livestock, poultry, and/or fish; and uses of such compositions to make medicaments. This invention is further directed to methods for determining the absolute configurations of zilpaterol enantiomers.