This review outlines the potential for developing a reliable transformation system for onions(Allium cepa).A summary of the onion tissue culture literature is presented along with descriptions of the gene transfer systems available. The most suitable regulatory sequences and selective genes that could be used for onion transformation are described, together with the problems which may be encountered following the integration into the particularly large genome of onion. The review proposes likely routes by which transformation and regeneration may be achieved, and suggests possible characteristics of onions which may be altered using such a technique.