The purpose of this study was to evaluate the validity of two different measures of physical activity under normal living conditions. The 24-hour physical activity diary method (24 HD) and accelerometer (Lifecorder) were analyzed. Total daily energy expenditure (TDEE) and daily varia tion of energy expenditure (EE) were compared employing the two measures in conjunction with the minute-by-minute heart rate method (Flex HR) in middle-aged people with a mean age of 57.9 yr (N =17), and in young people (college students) with a mean age of 23.5 yr (N=11) . The TDEE as measured by the 24HD and Lifecorder was 2576.4±514.7kcal·d^-1 and 1973.1±290.2kcal·d^-1 respectively. The TDEE as measured by the Flex HR method was 2718.3±625.5kcal·d^-1. The TDEE as measured by the Lifecorder method was significantly lower than that of the Flex HR method (p<0.01), The correlation coefficient (r) for the 24 HD and FlexHR measured values for TDEE (kcal/day) was 0.64 (p<0.01), and that for Lifecorder and Flex HR was 0.38. The daily variation of energy expenditure pattern measured by Lifecorder was similar to that of the Flex HR ; 24 HD measurements, on the other hand, were slightly lower than Flex HR measurements during the afternoon period. The 24 HD method was reasonably accurate in the testing. The daily variation of energy expenditure measured pattern by Lifecorder was similar to that of the Flex HR method ; but the fact that the TDEE results were underestimated suggests that the Lifecorder method has merit in the measurement of daily activity patterns. It follows from this that to improve measurement of the TDEE, it is necessary to modify the Lifecorder method of calculating the algorithm,