A local-equilibrium theory is developed and used to investigate the behavior of retained pH and ionic strength gradients formed on a strong-base anion-exchange column where both anion- and cation-forming buffering species are present. Analytical relations are presented for several simplified cases of practical interest and are used to illustrate factors governing the selection of the elution and presaturation buffers when retained pH and ionic strength gradients are employed for preparative protein chromatography.