In order to evaluate calcium requirements (RC) in Japanese elderly women, a calcium balance study was carried out in 9 osteoporotics (73.9 +/- 2.7 years old, mean +/- SE) and 9 normal elderly women (67.0 +/- 2.5 years old). Diet containing 700 mg/day of calcium were given for at least 1 week. Then, diets containing approximately 700 mg/day (722.5 +/- 91.9 mg/day) of calcium in the 1st week and 1,474 mg/day of calcium in the 2nd week were served. The amount of calcium intake to maintain zero balance, defined as daily RC, was 550.4 +/- 50.0 and 648.8 +/- 44.7 mg/day in normal and osteoporotic subjects, respectively. There was no statistically significant difference between these two groups. Although the recommended daily allowance (RDA) for the adult Japanese is 600 mg/day, our study suggests that RDA in the elderly Japanese should be 847 mg.