Since the first clinical use of tumour markers, quality assurance has been considered only in a restrictive manner, that is, as a surveillance of the analytical process. In other words, quality assessment was roughly viewed as a synonymous with quality control. This is not surprising, since tumour markers are almost exclusively assayed by radioimmunoassays, whose analytical performance were suboptimal in the 1970s. Furthermore, tumour marker concentrations in biological fluids were very low (in the ng range); in addition, primary standards were not available and dose-response curves were set up with conventional calibrators. Therefore, quality control programmes have become mandatory to restrict intra- and inter-laboratory variability.