A novel plant protein isolated from the underground bulbs of Scadoxus multiflorus, xylanase and a-amylase inhibitor protein (XAIP), inhibits two structurally and functionally unrelated enzymes: xylanase and a-amylase. The mature protein contains 272 amino acid residues which show sequence identities of 48% to the plant chitinase hevamine and 36% to xylanase inhibitor protein-I, a double-headed inhibitor of GH10 and GH11 xylanases.