The computational algorithm and the Prep-LEAR program have been performed on the basis of the LEA model of chromatography. This program intends for calculation of peak profiles in non-linear high-performance chromatography and uses unsimplified adsorption isotherm equations. The computational algorithm and program have been tested by applying these to experimental data of thymine adsorption under conditions of reversed-phase high-performance liquid chromatography. The results of numerical calculations for different sample size introduced agree satisfactorily with experimental data and show the characteristic properties of high-performance chromatography. The usefulness of the Prep-LEAR program was confirmed by predicting peak profiles in preparative adsorption chromatographic processes.