Ligand evolution was continued until the genetic algorithm was unable to generate more mutants, except STgrow4 with W=1.5 which was stopped arbitrarily after 220 generations as it did not selfterminate. The results for W=1, W=1.5 and W=2 are summarized in Table . The best docking energy obtained by using Autogrow4 was -9.6 kcal/mol. The same value, -9.6 kcal/mol, was obtained for STgrow4 with W=2. However, an improved value of docking energy, -10.2 kcal/mol was obtained for STgrow4 with W=1. Molecules with LogBB greater than 0.3 are predicted to be Blood-Brain-Barrier permeable. A comparison of the distributions of molecules generated by Autogrow4 and STgrow4, showed that for molecules with LogBB greater than 0.3, the best docking energy was -8.2 kcal/mol for molecules generated by Autogrow4, -9.0 kcal/mol for molecules generated with STgrow4 using W=1, -9.2 kcal/mol for molecules generated with STgrow4 using W=2 and -9.4 kcal/mol for molecules generated with STgrow4 using W=1.5.