Some considerations are given on the division into groups of the reference materials in the collection of the Central Research Laboratory, Amsterdam. A distinction is made between specimen or example materials and standard materials, depending on the quality of the information available. Furthermore the name 'standard objects' is suggested for more complex materials which may be used in studies regarding the ageing of materials. The criteria to which a material must answer before one can call it an example material or a standard material are discussed briefly, together with the way the materials can be used. A survey is given of the collection of the Central Research Laboratory. Some manufacturers or distributors of parts of the collection are mentioned.