A distinctive method of high-performance liquid calibration peak-area quantitation, called the standardless or absolute method, allows the absolute number of moles of the main amino acids found in twenty-six commercial fruit juices to be determined. The theory of the standardless model is briefly illustrated. The results found with this alternative method are compared with the reference procedure (calibration with external standards) by using difference plots and regression analysis. The presence of both systematic, constant, and proportional errors between the two methods is disclosed and discussed.