The adoption of procedures warranting the quality of the results obtained in the laboratory is of the utmost importance, whatever the reason these analyses are required for. We discuss some of the fundamentals of quality assurance, as recommended by the International Federation of Clinical Chemistry, IFCC. Procedures for the preparation of control and calibration materials, the evaluation of analytical methods and the assessment of laboratory performance by means of internal quality control procedures, including control charts, are reviewed. Finally, we report the organisation and the strategies use in programmes for external quality assurance for the determination of trace elements in biological fluids.