Measurement of fatty mass (%Fat) by the method of Nagamine, maximal aerobic power (MAP) according to the method of Margaria et al., blood pressure and serum lipids were carried out on 104 males and 169 females aged 20-49 years to provide a basis for the evaluation of obesity by %Fat. Obesrvation of food intake was also done by a routine questioning and parsonal interview to clarify the characteristics of subjects. The energy from fats were about 25% of caloric intake and the animal fat were about 49% of total fats intake in both sexes. In the case of males, significant correlations were found between %Fat and HDL-choresterol (HDL), triglycerids (TG) and diastolic blood pressure (DBP) . Values of %Fat calculated from each regression equation when HDL=35mg/dl, TG=150mg/dl and DBP=89mmHg were about 21%, 20% and 33%, respectively. The highest value of %Fat was 27.4% in males. About 86.7, % of subjects whose %Fat above 20% showed one or more abnormal values (HDL below 34mg/dl, TG above 15lmg/dl or DBP above 90mmHg) . The appearance rate was about 61.3% in the case of subjects whose %Fat within the range of 15-19.9%. However, significantly lower rate of about 31.0% was found in the case of subjecte whose %Fat under 15%. From these results, it is considered that man whose %Fat above 20% is called obesity and man whose %Fat within the range of 15-19.9% is called mild obesity. The appearance rates of abnormal HDL, TG or DBP were about 15.4% in the case of Fit Non-obese group (MAP above 40ml/ kg/min & %Fat under 15%), about 42.9% in the case of Unfit Non-obese group (MAP under 40ml/kg/min & %Fat under 15%) and about 66.7% in the case of Unfit Obese group (MAP under 40ml/kg/min & %Fat above 15%) . Differences of the appearance rates between Fit Non-obese group and other two groups were significant but not significant between Unfit Non-obese group and Unfit Obese group. Though 11 subjects who were prohibited the exercise test by medical check and 9 Fit Obese subjects were not involved in this calculation of the appearance rate, it is said that combined method of %Fat and other functional measure such as MAP etc, is also necessary to evaluate the obesity. In the case of females, significant correlations were found between %Fat and HDL, total choresterol (TC) and DBP. However, values of %Fat calculated from each regression equation when HDL=40mg/dl, TC= 243mg/dl and DBP=89mmHg were about 72%, 208% and 57%, respectively. However, the highest value of %Fat was only 47.1% in females. Difference of the appearance rates of subjects who showed one or more abnormal values (HDL below 39mg/dl, TC above 244mg/dl or DBP above 90mmHg) were not found significantly even between the highest %Fat group (38.6±4.1%) and the lowest %Fat group (17.0± 2.1%) . Therefore, in the case of females, a cutoff point of obesity and non-obesity was not found. These results indicate that effects of the increase of body fat or physical inactivity on serum lipids and blood pressure are considerably moderate in females.