Recent studies have demonstrated the feasibility of using ultrafiltration with a stereospecific binding agent in free solution to separate chiral molecules. The objective of this study was to develop an improved understanding of the key factors that determine the effectiveness of this type of chiral separation. Experiments were performed using a model system of bovine serum albumin as a stereospecific binding agent for the amino acid tryptophan. Batch ultrafiltration data showed strong stereospecific binding of L-tryptophan with a selectivity of 11 at low amino acid concentrations. Actual separations were performed using a constant volume diafiltration system to wash the less strongly bound isomer through the membrane. The diafiltration process avoids problems associated with the accumulation of retained species during filtration and makes it possible to achieve higher purification factors. The L-tryptophan was recovered in the retentate with final purity greater than 90% at 60% yield. Model calculations performed using the equilibrium binding constants for the two stereoisomers were in good agreement with the data. Simulations were used to examine the performance of this membrane system for chiral separations.