Affinity chromatography and parametric pumping were combined to reduce trypsin concentration in an aqueous solution. The trypsin inhibitor, chicken ovomucoid, was covalently bonded to Sepharose 4B beads. A solution was cycled over this packing in a column at a low pH in one direction followed by a high pH in the other direction. Trypsin retention was favored at the high pH and elution at the low pH. The decrease in trypsin concentration at one end of the column was fitted to an equation derived from the equilibrium parametric pumping model and was a function of the pH limits imposed on the column. Separation was much less than predicted by equilibrium data, but the equation based on trypsin reduction agreed with the α-chymotrypsin-trypsin separation.