The important role of many carbohydrates on calcium metabolism has been demonstrated by FOURNIER and DUPUIS. Starch, however, neither influences the absorption nor the retention of calcium. Less is known about the effects of sucrose. In this study the influence of starch on calcium metabolsim has been compared with that of sucrose. Male weanling Wistar rats were divided into three groups according to their diets. The first group received a refined and well-balanced diet (except for the absence of vitamin D), containing 68 p. 100 of starch. The second group received the same diet except sucrose was substituted for the starch. The third group received the same diet as Group 1, with the addition of vitamin D. Plasma calcium citrate and urinary citrate and calcium were determined. At the age of 2 months after one night of fasting, each group of rats was injected intraperitoneally with a 1 ml, aqueous solution containing 1 mg calcium and 0, 6 mu Ci45Ca. Twenty-four hours later the animals were sacrificed and the calcium femur percentage, radioactivity p. 1,000 of the injected dose of 45Ca, and specific radioactivity were determined. When performance data from Group 3 were compared to Group 1 and Group 2, the following results were obtained: --Group 1 (starch diet without vitamin D) had very low plasma calcium levels; urinary calcium, plasma citrate and urinary citrate levels were lowered, and the calcium femur percentage was smaller. Bone avidity for calcium was found. --Group 2 (sucrose diet without vitamin D) had normal plasma calcium levels. Urinary calcium and citrate and plasma citrate did not show significant differences from those of animals receiving vitamin D. No significant differences were found in the specific radioactivity and radioactivity p. 1,000 of the administered dose. Contrary to starch, sucrose maintained calcium homeostasis, and apparently, normal ossification, although the femur was lighter than those of animals receiving vitamin D. Further work is necessary to determine whether the fructose component of the sucrose molecule is responsible for the increased calcium utilization and, if so, what levels of ingestion are necessary for this activity.