Developments in the biological sciences in the last three decades have revolutionized mankind's ability to manipulate the genetics, cell biology and physiology of biological organisms. These techniques, collectively termed biotechnology, create the opportunity for modifying domestic animals in ways that markedly increase the efficiency of production. Among the procedures being developed for animal production systems are marker-assisted selection of specific alleles of a gene that are associated with high production, production of transgenic animals, superovulation and embryo transfer, in vitro fertilization, embryo sexing and clonıng, production of large amounts of previously-rare proteins through use of genetically-engineered bacteria or other cells, and identification of new biologically-active molecules as potential regulators of animal function. To date, most uses of biotechnology have concentrated on problems of general relevance to animal agriculture rather than specific problems related to livestock production in hot climates. However, it is likely that biotechnology will be used for this latter purpose also. Strategies to increase disease resistance using marker-assisted selection, production of transgenic animals expressing viral proteins, and recombinant cytokines to enhance immune function should prove useful in reducing the incidence and severity of various tropical diseases. Additionally, there are methods to reduce effects of heat stress on oestrus detection and establishment of pregnancy These include remote sensing of oestrus, ovulation synchronization systems and embryo transfer. More research regarding the physiological processes determining heat tolerance and of the pathways through which heat stress alters physiological function will be required before molecular biology techniques can he used to reduce the adverse effects of heat stress on animal production.