||The purpose of the present study was to compare the thermal responses of the body between bathing in warm sea water and fresh water, and also to further examine how the chemical components in sea wate...r affect the thermal responses of the body when bathing in warm sea water. The thermal responses were based on an examination of the rectal, skin and mean body temperatures at 0, 10 and 20 minutes of bathing as well as at l0, 20, 30 and 40 minutes in post-bathing recovery on land. Six healthy men were the subjects of this experiment, and they were on average 33.3±2.6 in age, 168.8±6.3cm in body height, 69.6±11.9kg in body weight, and had a body fat ratio of 16.3±4.5% on average. The subjects bathed in sea water and fresh water for 20 minutes and thereafter recovery on land for 40 minutes, respectively. The experiment was conducted under water at a temperature of 38.5℃ during the bathing. In all subjects, the rectal temperature increased during bathing and thereafter decreased gradually during recovery on land. Bathing in sea water showed significant increases in the rectal temperature at 20 minutes during bathing and at 10 minutes during recovery on land. The mean skin temperature showed a continuous increase during bathing and a rapid decrease during the first 10 minutes of recovery on land, followed by a gradual decrease thereafter. No significant differences were observed in the mean skin temperature between sea water and fresh water. The mean body temperature also showed a continuous increase during bathing and a rapid decrease during the first 10 minutes of recovery on land, and a gradual decrease thereafter. The mean body temperature in sea water showed significant increase compared with that in freash water during the examined time from the first 10 minutes after bathing to 40 minutes after recovery on land. From the above results it was proven that the thermal responses of the body were higher when bathing in sea water than when bathing in fresh water. This was indicated as a result of the tunicate effect of the chemical components of sea water. Moreover, the amount of sweating judged from body weight loss indicated that bathing in warm sea water also demonstrated a tendency to control hydromeiosis.