The albumin fraction of sunflower seed (Helimthus unnuus, cv. Mirasol) is a family of water soluble basic polypeptides which constitutes about 20% of the seed proteins. This fraction, isolated by selective isoelectric precipitation of globulins, has been studied in detail by sodium dodecyl sulphate gel electrophoresis, non equilibrium pH gradient electrophoresis and combination of these techniques using non reducing and reducing conditions. The molecular mass of the main polypeptides was markedly different between unreduced (12,000 to 16,500 g . mol-') and reduced form (l0,OOO to 18,000 g . mol-I). As shown by NEPHGE mobility of these polypeptides was also altered by reduction. From these results and other observations is concluded that the stability of the globular structure of some polypeptides is dependent on the presence of intact disulphide crosslink(s). By multidimensional gel electrophoresis it was shown that the polypeptide components of each molecular mass classes displayed a high heterogeneity in net charge. Thus ion exchange chromatography procedures allowed only partial separation of different polypeptidic groups. Their amino acid composition shows that some of these fractions are, on the basis of their lysine and sulphur containing amino acids, of nutritional interest.