Method, tool and experiences of the requirement specification method RELSPEZ are presented. RELSPEZ is based on a relational data model and expresses input and output of every atomic processing of an application function on parts of the data model. Processing is described in a semi-formal manner. The method RELSPEZ was developed in an industrial software project and also applied there. The tool for running it is PET/X 116o. After a pilot application of RELSPEZ – and other specification methods – was recommended only to be used for incomplete specifications of user-relevant requirements. The reasons for such a revised use of the method are discussed.