One important aspect of product-related environmental protection is environmentally safe product recycling or disposal. This is possible only with the knowledge of the substances contained and the potential hazards to health and to the environment that they represent. Therefore@ the manufacturer should know which environmentally relevant substances are contained in his products. Additionally@ he should know the distribution and the concentrations of these substances. He should be able to give the required information to those who need it. The flow of information on material content involves several parties. This guideline is not prescriptive. It is rather written to assist companies which have to develop materials declaration questionnaires for products@ for instance as part of purchase specifications. It intends to increase the harmonization and the comparability of the various questionnaires. This is supposed to lead to cost reduction@ both for those sending questionnaires and for those answering them@ but it must be kept in mind that the possibilities for harmonizing the materials declaration questionnaires are limited because of the differing needs of those requiring information@ and because of the continual changes of the hazardous materials lists.