This research project addresses several physiological problems that have emerged from recent studies of diving behavior in king and emperor penguins. Foremost is the seemingly consistent pattern of both species to make frequent, exceptionally long and deep dives. The emperor penguin is the most suitable species for measuring physiological variables related to breath-hold limits and oxygen management, while diving voluntarily. Some of these variables are muscle and blood oxygen levels and blood chemistry. The king penguin is most suitable for studies of the effects of compression on gas exchange. Some measurements will be blood oxygen and nitrogen contents during the course of simulated dives to 200 m. Other experiments will determine the energetic output of diving, the morphological and behavioral development of diving of incipient fledglings and specific measures of foraging success. The results of this work will be relevant not only to diving physiology, but will also comprise an essential element in understanding energetics and trophic relationships in the polar ecosystem.