The goal of this study was to identify and characterise the major allergen(s) of sesame seed. Detection of specific IgE to sesame proteins was performed with Pharmacia CAP System and Western blotting, after separation of sesame proteins by SDS-PAGE, using sera from 28 subjects diagnosed as allergic to sesame. The major allergen was separated by gel filtration chromatography and identified by selective proteolysis followed by peptide sequence analyses, employing electrospray-ionization mass spectrometer. Twenty-four of the 28 subjects had sesame-specific IgE. A 14 kDa protein belonging to the 2S albumin family was recognised by 22 of the 24 sera used. Subjecting the 14 kDa after HPLC separation to proteolysis with Lys C yielded 3 peptides, but only one reacted positively in the dot blot test. This peptide, corresponds in the whole protein chain to residues 24-94. The reactivity of the 14 kDa protein with most of the sera indicates that this is the major sesame allergen, later identified as 2S albumin precursor; and its peptide which reacted positively in the dot blot test evidently contains an epitope(s). Some minor sesame allergens, of higher molecular weight, were also revealed.