The accreditation of laboratories is increasingly demanded as evidence of the reliability of the data they produce, and is therefore of strategic importance to laboratories for maintaining and/or increasing their level of competitiveness. Although accreditation is increasingly developed in sectors such as food quality control, it is less common for environmental laboratories. A very important feature in quality-assurance practice (whether related to accreditation or not) is the use of reference materials, which are invaluable tools for the verification of quality control in environmental analysis. Some problems are discussed which relate to the use of reference materials by environmental laboratories and their linking to accreditation.