Experimental values of the partition constants between brain and blood, log K(Br/Bl), of a series of compounds including simple organic molecules and some drugs were correlated with experimental values of the partitioning between sodium dodecylsulfate (SDS) micelles and water, log K(SDS/w). From a training data set of 21 compounds a good linear correlation was found and a function was derived to relate log K(Br/Bl) with log K(SDS/w). This correlation together with a simple group (fragment) contribution method that is proposed to calculate log K(SDS/w) provided the basis for a succesfull calculation of log K(Br/Bl) values for several compounds outside the training dataset