The invention refers to a fully human miniantibody (scFv), called Erbicin, specific for the receptor ErbB2, with a pharmacological, in particular antitumour, activity. It has been obtained from a larger fagmidic library (Griffin 1.) (19) of human synthetic scFv by panning (affinity selection on antigen) carried out on live cells that express various levels of ErbB2. The invention relates also to the DNA and aniino acid sequences of said antibody, to the procedure for isolating it, to its use in therapy.