AbstractCore temperature was determined in two king penguins living in the wild at Ile de la Possession, Crozet Archipelago, using implantable four-channel temperature loggers. Core temperatures derived from bird no. 1 (sensor placed under the sternum, in the vicinity of the liver and upper stomach) were closely correlated with diving activity (as determined by an external light recorder), and ranged from 38.3C, (on land) to a minimum of 37.2C during a dive. Core temperatures measured in bird no. 2 showed that temperatures near the heart were generally 1C lower than those under the sternum or in the lower abdomen. Core temperatures declined continuously during dives (by 0.8, 1.2 and 2.7C in the lower abdomen, under the sternum and near the heart, respectively) and showed precipitous drops to 35C, probably associated with ingestion of food. Temperatures measured near the heart fluctuated over a period of 288s, corresponding to the duration (from the literature) of the surface/dive cycle. The relevance of these findings with respect to diving physiology, blood perfusion of tissues, tissue metabolism and aerobic dive limits is discussed.