In 1996, maize, cotton, and potato farmers in the USA became the first farmers in the world to grow transgenic insect-resistant cultivars. These cultivars contain genes from the bacterium Bacillus thuringiensis (Bt) that encode insecticidal proteins known as delta-endotoxins. Delta-endotoxins have two properties that are essential for toxins used in transgenic crops: they are highly toxic to certain insect pests, and they are generally safe for human consumption (NRC 2000). Bt crops have been a large commercial success. In 1999, 11.7 million ha of Bt crops were grown by farmers in 10 countries, including Australia, Canada, China, South Africa, Spain, and the USA (James 1999). Many laboratories around the world have transformed rice with Bt genes and have evaluated their effectiveness under greenhouse conditions (e.g., Cheng et al 1998, Datta et al 1998, Maqbool et al 1998). No Bt rice varieties have yet been released to farmers, but field testing began at two sites in China in 1998 (Datta 1999, Ye et al 2000). The target pests for control by Bt rice are caterpillars, most importantly the yellow stem borer (YSB, Scirpophaga incertulas), the striped stem borer (SSB, Chilo suppressalis), and leaffolders such as Cnaphalocrocis medinalis. It has not been possible to produce rice with high resistance to these pests through conventional breeding, although short-duration semidwarf varieties are generally less damaged by stem borers than are traditional varieties (Khan et al 1991).Genetic engineering with Bt genes is a powerful technology for protecting crops against some kinds of insects. Bt cultivars, however, have the same weakness as many other insect control technologies: insects can evolve resistance to them, thereby eliminating their effectiveness.1 Insects have evolved resistance to all classes of widely used insecticides, including Bt products that are applied as sprays (Frutos et al 1999). Insects have also adapted to numerous resistant crop varieties produced through conventional breeding. Notable examples in rice include the brown planthopper, Nilaparvata lugens (Heinrichs 1986), and the Asian rice gall midge, Orseolia oryzae (Bennett et al 2000).The problem of insect adaptation to insecticides and resistant cultivars results in substantial costs to society, as crop failures, environmental damage, and loss of useful products. This has stimulated extensive research on the genetic and biochemical basis of resistance, and the development of 'resistance management' strategies that can extend the effectiveness of insecticides and cultivars. In this review, we describe some practical steps that can be taken to delay the evolution of pest resistance to Bt rice.