The selectivity of different phenyl HPLC stationary phases has been evaluated with respect to structurally similar steroids, including sapogenins of plant origin. A column packing containing a biphenyl ligand was best at separating species that differed with respect to their degree of unsaturation. A diphenyl phase performed better than the biphenyl column in separating steroid epimers, but the best phase for epimer separation was octadecasilyl-bonded silica. The various mechanisms responsible for these results are discussed.