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Bile salt‐stimulated lipase (BSSL) in human milk exists in multiple molecular forms and it has been shown that approximately one‐third of lactating mothers secrete two forms. Aim: to determine the structural features of BSSL that may give rise to this heterogeneity. Methods: Oligosaccharides present in the proline‐rich region in the C‐terminus of BSSL were investigated using deglycosylating enzymes and lectin affinity probing to determine the origin of the multiple molecular forms. Results: It was found that the variability in the molecular mass of BSSL is due predominantly to glycosylation. The molecular forms contain similar sugar chains; all forms possess the core disaccharide Galβ1‐3GalNAc and β‐D‐galactose, fucose linked at α1‐6 and sialic acid linkage α2‐3 to galactose. Conclusion: The molecular mass difference in the BSSL molecular forms cannot be attributed to the type of carbohydrate moiety in the sugar chains of the N‐ and O‐linked sites suggesting that the differences arise from the extent or quantity of glycosylation. The oligosaccharides in the C‐terminal region contain Lewis x and b and, less prominently, Lewis a antigenic structures. Owing to the presence of these blood‐group‐related antigenic determinants, the C‐terminal region of BSSL may have an adhesive function in cell‐cell interactions.

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