The chromatographic capacity factors (k(IAM)) of 23 structurally diverse drugs were measured by the immobilized artificial membrane (IAM) phosphatidylcholine chromatography for the prediction of blood-brain barrier (131313) penetration. The k(IAM), was determined using the mobile phase consisting of acetonitrile:DPBS (20:80 v/v) and corrected for die molar volume of the solutes (k(IAM)/MWn). The con-elation between k(IAM)/MWn and CNS penetration was highest when measured at pH 5.5 with the power function of n = 4. This in vitro prediction method was validated with 7 newly synthesized PDE-4 inhibitors. The relationship between in vivo plasma-to-brain concentration ratios and in vitro CNS penetration was excellent (r = 0.959). The developed in vitro prediction method may be used as a rapid screening tool for 131313 penetration of drugs with passive transport mechanism, with high success, low cost, and reproducibility.