The mammalian response to hypothermia is increased metabolic heat production, usually by way of muscular activity, such as shivering. Seals, however, have been reported to respond to diving with a hypothermia, which in other mammals under other circumstances, would have elicited vigorous shivering. In the diving situation shivering could be counter productive, since it obviously would increase oxygen consumption and therefore reduce diving capacity. We have measured the electromyographic (EMG) activity of three different muscles and rectal and brain temperature of hooded seals (Cystophora cristata) when exposed to low ambient temperatures in a climatic chamber, and when performing series of experimental dives in cold water. In air the seals had a normal mammalian shivering response to cold. Muscles were recruited in a sequential manner until body temperature stopped dropping. Shivering was initiated when rectal temperature fell below 35.3 ± 0.6°C (n=6). In the hypothermal diving seal, however, the EMG activity in all the muscles that had been shivering vigorously prior to submergence was much reduced, or stopped altogether, while it increased again upon emergence, but was again reduced if diving was repeated. It is concluded that shivering is inhibited during diving to allow a decrease in body temperature, whereby oxygen consumption is decreased and diving capacity is extended.