The electrokinetic behaviour of compact ceramic surfaces is mainly characterised by streaming-potential measurement using flow parallel to the surface. For these measurements the electrokinetic analyser (EKA) is commercially available. Often this method shows experimental difficulties. In view of filtration-membranes characterisation the process determining effect derives not only from the surface. The open porosity of the membrane as a whole also influences the interaction with charged species to be filtrated. A new method was developed closely related to real filtration: A `flow-through' potential measurement. Suspensions are nowadays characterised using an electroacoustic method. To link the electrokinetic results measured on suspensions to measurements on compact surfaces a new 'electroacoustic-surface-potential' measurement was tested. It is obvious that the electrokinetic behaviour of compact ceramic cannot be derived from suspension measurement. The properties of the electrically chargeable M-OH groups on the surface is changed during thermal treatment. (C) 2003 Elsevier Science B.V. All rights reserved.