Eggs of Dermochelys coriacea were incubated in the laboratory at different constant temperatures between 27 and 32°C up to hatching. The genital system of 72 neonates and 11 embryos was dissected and processed for histological study. All the individuals from the 27, 28 and 28.75°C incubations were phenotypic males. In the testes, the medulla was voluminous and very dense, composed of many epithelial cords, some enclosing germ cells, whereas the surface was covered by a thin layer of epithelial cells between which germ cells were still visible. The Müllerian ducts were in the process of regression. In all the individuals from eggs incubated at 29.75, 30.5 and 32°C, the gonads were somewhat longer than testes but were considerably reduced in width and thickness. The medulla was strongly inhibited, showing similar epithelial cords but much less numerous than in testes. The epithelium of the gonadal surface was pseudo-stratified and enclosed germ cells which had not enter meiotic prophase as in typical ovarian cortex. The Müllerian ducts were complete. These individuals were classified as potential females. These results show that temperature influences sexual differentiation of the gonads of Dermochelys coriacea and indicate that the threshold temperature (or pivotal temperature) lies between 28.75 and 29.75°C. They also reinforce fears about masculinising turtle populations by incubating eggs at cool temperatures in artificial hatcheries.