A water-soluble protein component, A, has been found which appears without exception at a higher concentration in Triticum aestivum than in T. durum. Quantitation of A is achieved by referring the height of densitogram peak A to the height of peak B, which corresponds to a second component that is present in all varieties studied from both species. Extreme valúes of peak height ratio (PHR) in both species are tentatively established. On the basis of these valúes, the máximum and minimum possible contents of T. aestivum in a mixture are expressed as a function of PHR. All the varieties of T. aestivum studied are detected when they contribute more than 60% to the mixture. In over 90% of all possible binary combinations between varieties of T. aestivum and T. durum, the máximum proportion of undetected T. aestivum has been 30%