The problems arising from increasing use of commercial kits in radioimmunoassay (RIA) and related fields are discussed. The problems arising in various RIAs differ according to the substance under test. The quality of individual components is often good, although methodology is often not optimal and contains short-cuts, which although commercially attractive, can lead to erroneous values and poor sensitivity and precision. Minor modification of methodology often leads to major improvements in sensitivity and precision, and this has been demonstrated in the case of three digoxin kits employing antibody-coated tube techniques and in four kits for thyrotropin (TSH) using different techniques. It has also been noted that in many imported quality control sera from the USA no values have been ascribed to European kits for the components listed, thus reducing these sera to the function of precision control. The deductions from this study are that a standardization of kit components and assay methods is desirable in order to allow comparison of results between laboratories using different kits.