Several chitin-binding proteins were isolated from the "bottom fraction" of Hevea brasiliensis (Müll.) Arg. latex. One of these chitin-binding proteins is hevein, a small monomeric protein which strongly resembles the lectin from stinging nettle (Urtica dioica L.). Like the latter, hevein showed strong antifungal activity against several fungi in vitro. The possible involvement of this protein in the defense against invasion by potentially pathogenic fungi is discussed.