A novel countercurrent chromatographic technique is described for the preparative separation-with excellent resolution-of up to multigram quantities of organic acids. This separation is accomplished by addition of a simple acid (e.g., trifluoroacetic acid) to the sample solution or stationary phase, followed by isocratic elution with a basic mobile phase. The acids elute as well-resolved rectangularly shaped peaks. This technique should rind widespread application in any organic chemistry laboratory for the separation of crude mixtures and for the purification of isolated acids.