[Principles and value of biochemical methods of analysis]

Biological systems and biological reagents like binding proteins, receptors or antibodies are increasingly used for qualitative and quantitative analysis of hormonally active substances. Due to their exquisite specificity and their high affinity constants reliable measurements in the femtomolar range are possible. However, interpretation of the results of such sensitive assays requires knowledge about the specific characteristics of these tests. In general, complex systems measure biological activities, but are cumbersome and often not very sensitive. For routine purposes competitive and non-competitive protein binding assays are preferable. In combination with adequate quality control, the results are clinically useful. these aspects are discussed and some examples are given. Future improvements should be made possible by the development of standardized biological reagents.