Rectal temperature, skin temperature and oxygen consumption were measured in five women divers during diving under two conditions a) wearing a cotton bathing suit and b) wearing a diving suit and the following results were obtained. 1. The duration of the diving period was 30 min with the cotton bathing suit whereas it was above 120 min with the diving suit. 2. The average rectal temperature fell to 34.5℃ after 30 min of diving with the cotton bathing suit. On the other hand, with the diving suit, immediately after submersion, the rectal temperature rose about 3℃ and remained at about 39℃ throughout the diving period of 120 min. 3. Average mean skin temperature during diving was 11℃ and 21℃ with cotton bathing suit and with the diving suit, respectively. The mean body temperature fell to 25℃ with the cotton bathing suit while it reached 32℃ with the diving suit at the end of each diving period. 4. Oxygen consumption during diving was three fold of the pre-dive level with the cotton bathing suit but it was two fold with the diving suit. 5. Total extra heat loss was 323 kcal during 120 min of diving with the diving suit. On the contrary, with the cotton bathing suit, it was 528 kcal for 30 min. These results may suggest that the prolongation of the diving period with the diving suit is primarily due to maintenance of core temperature at more or less physiological level as a result of reduction in conductive heat loss from the body surface to the water and the Preferential distribution of blood in the core area.