We attempted to propose the equation of assessing the functional status of elderly adult Japanese men. A number of physical and motor performance measurements were collected from a group of 104 male volunteer subjects (mean age 76.4 +/- 5.8 years). Factor analysis with varimax criterion was applied to all the data. Five factors extracted were interpreted as follows: (1) coordination of the body, (2) flexibility of the trunk, (3) static balance, (4) muscular strength and endurance, and (5) cardiorespiratory fitness. Furthermore, the factor score was computed for each individual by each factor. Each of the five factors were weighted in accordance with its relative contribution to the total variance (or the size of eigenvalue). The weighted combination of factor scores was summed to generate an index of functional status (IFS). Next, IFS scores were computed for each individual and normalized to T scores. Then, a multiple linear regression analysis was performed with the factor analytically derived IFS scores as the dependent variable: IFS = -0.625X1 + 0.604X2 + 0.346X3 + 0.223X4 + 0.465X5 + 0.082X6 + 0.114X7 + 0.199X8 + 0.019X9 + 0.071X10 + 19.76; where X1 = walking around two chairs in a figure 8 (sec), X2 = manipulating pegs in a pegboard (num), X3 = vertical jump (cm), X4 = sit and reach (cm), X5 = estimated maximal oxygen uptake (ml/kg/min), X6 = balancing on one leg with eyes open (sec), X7 = grip strength (kg), X8 = trunk flexion from a standing position (cm), X9 = leg muscle endurance in a semi-squat position against a wall (sec), and X10 = balancing on one leg with eyes closed (sec) Thus, information on the 10 variables from five domains was statistically combined to a single score. The above equation was cross-validated in the other group of elderly men (n = 54). The mean IFS obtained for this group (50.0 +/- 8.3) was not significantly different from the validation group (50.0 +/- 10.0). It is apparent that the IFS has the potential to serve as another useful measure of high order, daily living activities.(ABSTRACT TRUNCATED AT 250 WORDS)