The predicted expansion of plant genetic engineering has occurred since publication of the Spinks Report, but routes to profit have emerged much more slowly than the media predicted. The U.K. made a strong start in the science but its position relative to the U.S.A. has declined because of the relatively massive investment in the U.S.A. by industry and the public sector. An impressive list of plant species have been transformed with new genes over the past few years. Of relevance to agriculture, genes have been identified, isolated, characterized, reconstructed and inserted into plants that confer tolerance to some leading herbicides, insect pests and viruses. Some field trials of the engineered plants have been carried out. Field trials of genetically engineered potato plants have been undertaken in the U.K. The conditions under which genetically engineered plants are to be released into commercial agriculture is currently a very important topic of debate. The detection of favourable genotypes in plant breeding programmes is currently time consuming and expensive in some instances. The ability to assay genetic variation in all regions in the genome by restriction fragment length polymorphism mapping is providing promise to plant breeding programmes for identifying favourable genotypes.