Analysis by two dimensional electrophoresis (NEPHGE × SDS-PAGE) of proteins extracted with cold SDS solution from starch granules isolated from flour of the soft wheat cv. Galahad showed the presence of two very basic, approx. M r 15 k polypeptides with mobilities very similar to those of the surface-active, lipid-binding proteins, puroindoline-a and puroindoline-b. Whereas the puroindoline-a component predominated in the flour extract, the two analogous polypeptides extracted from isolated starch granules appeared to be present in similar amounts. When the starch proteins were fractionated by Triton X-114 extraction and phase partioning, the puroindoline-like polypeptides were found in the detergent-rich phase, as would be expected for puroindoline proteins. Purification of the Triton X-114-fractionated proteins from cvs. Galahad and Norin 61 by gel filtration and cation exchange chromatography allowed the separation of three polypeptides, the first having a slightly lower mobility on SDS-PAGE than the other two. The N-terminal sequence of the first 15 amino acids of the first of those proteins isolated form cv. Norin 61 was identical to those of 0·19 and 0·53 alpha -amylase inhibitors, whereas the N-terminal sequences of the second and third were identical to those of puroindolines-a and -b, respectively, apart from the eighth amino acid of the puroindoline-b homologue, which was glycine in the starch protein, whereas it is reported to be serine in puroindoline-b. The similarities between the electrophoretic, detergent fractionation and N-terminal sequence properties of two of the cold SDS-extractable starch friabilin polypeptides and those of puroindolines-a and -b strongly suggest that friabilin comprises a mixture of proteins in which the puroindoline polypeptides are important components. The amino acid sequence data indicate that some alpha -amylase inhibitor proteins are also significant components of friabilin. The reason for the differential binding of these proteins to the surfaces of hard and soft wheat starch granules remains to be found, but elucidation of that reason may be important in defining the molecular mechanisms by which endosperm texture variation is controlled.