The optical resolution of racemic tryptophan was performed by ultrafiltration using the BSA solution system. The pH of the feed solution had a strong influence on the complexation constants between BSA and tryptophan, especially for L-tryptophan. The complexation constant for L-tryptophan reached a maximum value at pH 9 (K-L = 110,000), varying by 2 orders of magnitude in the range from pH 6 (K-L = 1000) to pH 11 (K-L = 21,000). Smaller variations of the complexation constant of D-tryptophan were observed. Based on these data, the recovery and the purity of the permeate were optimized by a proper control of the physicochemical parameters of the feed solution (essentially pH and initial concentrations). In one stage, 91% purity with a 89% recovery of D-tryptophan has been easily obtained with a high permeation rate (6.3 x 10(-4) mol.m(-2).s(-1) at 1.5 bar).