Some results from a research program to the cross-flow-filtration are presented. The experiments were carried out using a rotational shear gap filter for filtering fine china clays in a pa ra meter field of low solid concentrations and high stream velocitys. Details of experiments are given and results are discussed. It is shown how the pressure and the particle diameter can influence the particle deposition at the begin of filtration. This paper gives a contribution for determination on validity limits of models.