Proteinaceous materials in musts were separated by high performance liquid chromatography (HPLC) on the basis of molecular size, using a TSK G3000 SW column. The size and the nature of the various proteinaceous fractions were estimated by comparing them with protein standards and proteins isolated from the must by gel-chromatography on a Sephadex G-100 column. Seven fractions of different molecular weight: (I) > 300 000; (II) 83 000; (III) 18 700; (IV) 15 000; (V) 6600; (VI) 4200; (VII) <255, were obtained. Among these the most abundant was fraction VI with a relative percentage of 36·4%. Although this method did not completely separate all the proteinaceous fractions in the must, it showed a significant development in this field, due to its high level of resolution and its speed, when compared with traditional methods.