Reference values on concentrations of chemical components in body fluids/tissues serve as indispensable guides for the interpretation of results of biochemical investigations. They provide the criteria necessary for deciding if laboratory results obtained on patients indicate the presence of pathological states or abnormal metabolism. However, in order for reference values to fulfill their expected function, their preparation must take into account the multitude of factors that are now known to have influence on their magnitude and distribution. Ignorance of the effect of such factors can lead to misuse of reference values or preparation of reference data which are of limited use and sometimes misleading. On the other hand, it must be emphasised that even when comprehensive sets of reference values are available, it is necessary to take into consideration all relevant clinical information, including treatment and other diagnostic procedures on the patient before attempting interpretation of any laboratory data. In view of the increasing number of factors that can affect laboratory results, the clinical chemist has an increasingly important role in assisting his clinical colleagues in the interpretation of results and ensuring the intelligent and proper use of reference values for patient diagnosis and management, through comprehensive reporting and education.