The competitive adsorption isotherms of praziquantel enantiomers on microcrystalline cellulose triacetate were determined by concentration pulse chromatography. A model comprising a non-selective linear term and a selective first order improved Langmuir term was found to fit the data excellently. It is postulated that this chiral stationary phase consists of two types of binding sites: one responsible for the chiral, selective interactions and one responsible for the achiral, non-selective interactions of the enantiomers with the stationary phase. The selective sites are easily saturated compared to the non-selective sites, accounting for the experimental observation of lower separation efficiency at higher enantiomer concentrations.