The possible roles of heat shock proteins in normal develop-§ment in animals, plants and model systems and the effects§microorganisms and the effects of elevated temperature on§developmental programs are comprehensively treated. All re-§levant aspects of heat shock genes in normal and abnormal§development are covered all of the major biological systems§currently used to study the developmental biology of heat s-§hock genes included. Heat is a medically significant terato-§gen in humans and (other) animals. The heat shock response§itself is developmentally regulated and is likely to be pro-§tective in the developingembryo. In addition to roles in§stress responses, heat shock genes are differentially ex-§pressed during normal development in germ tissues and fur-§ther in the specialized cell types of somatic tissues such§as the mammalian brain. Heat shock genes are regulated du-§ring the cell cycle and heat shock promoters are being used§in ectopic expression systems to study the functions of§particular genes during development.