Four male volunteers served as subjects for studies under hyperbaric helium-oxygen environments at 16 bar and 31 bar (simulated saturation dive). Tympanic membrane temperature, rectal temperature, ventilatory gas temperature, expiratory volume, respiratory frequency and cardiac frequency were measured during Cold Gas Inhalation (CGI : 20min) and recovery period (20min) in a warm hyperbaric chamber. Dyspnea and fall in deep body temperatures were evident during CGI (inspired gas temperature : 6°C at 31bar, 7°C at 16 bar). The change of tympanic membrane temperature during CGI and recovery period was more definite than rectal temperature. This phenomenon was induced by remarkable direct heat exchange between environment and body core, owing to high heat conductivity and high heat capacity of respiratory gas. Concerning safety and physiological functions of the deep sea diver and human exposed to hyperbaric helium-oxygen environment, not only rectal temperature monitoring is very important but also tympanic membrane temperature monitoring.