This article presents a method for a comparative assessment of process technologies from a cleaner production point of view as well as the results of testing this method in practice. Based on these results and on an analysis of existing technology information systems, an estimation is made of the general possibilities and limitations of a comparative assessment of process technologies from a cleaner production point of view. Finally, the resulting consequences for the definition of `best available techniques' in accordance with the new EC Council Directive Concerning Integrated Pollution Prevention and Control (IPPC) are discussed. This article argues that apart from the difficulties related to the valuation of different kinds of materials and energy a major limiting factor is caused by the fact that the function of a production has to be defined very precisely to enable a comparison between different types of process technologies in sufficient detail.