The Royal Society report, Genetically modified plants for food use (1998), concluded that the use of genetically modified (GM) plants potentially offered benefits in agricultural practice, food quality, nutrition and health, but that there were several aspects of GM technology which required further consideration.  We recognise that there is public concern about GM technology, particularly with respect to the safety of GM food for human consumption and to the possible effects of the technology on the environment.  Since the 1998 report there has been new research which the working group has evaluated.  This update focuses on the effects that GM foods might have on human health and the use of the principle of substantial equivalence in GM food safety testing.