The presence of marker genes encoding antibiotic or herbicide resistances in genetically modified plants poses a number of problems. Various techniques are under development for the removal of unwanted marker genes, while leaving required transgenes in place. The aim of this brief review is to describe the principal methods used for marker gene removal, concentrating on the most recent and promising innovations in this technology. (C) 2002 Editions scientifiques et medicales Elsevier SAS and Societe francaise de biochimie et biologie moleculaire.