||The purpose of this study was to observe the characteristics of thermoregulatory responses during exercise in young labile hypertensives. A young labile hypertension group (LHG) (n=6) and the control ...(CG) (n=6) group pedalled a Monark bicycle ergometer at the work rate of 600 kpm/min for 20 min in the temperate environment. Tympanic and skin temperatures, heart rate, systolic blood pressure and sweating responses were measured of subjects in both groups during the work. The result is summarized as follows : 1. The mean skin temperature during exercise showed an increased rate in LHG than in CG. 2. The subjects in LHG at rest represented sinus tachycardia in comparison with CG, but no significant difference was observed in the increases of heart rate during exercise in both groups. 3. The increased rate of systolic blood pressure during exercise was higher in CG compared with LHG. 4. The relationship between body temperature (tympanic and mean body temperatures) and heart rate exhibited a high correlation coefficient in LHG during exercise and recovery periods. 5. There were no obvious differences between LHG and CG in sweating responses and heat storage during exercise. These results seem to suggest that thermoregulatory responses during exercise in hypertensives are qualitatively different from those in normal subjects, and these will offer interesting insights in a further consideration of exercise therapy in hypertensive.