The long-term and short-term influence of large oral doses of ascorbic acid on the urinary excretion of calcium has been investigated. In the first experiment, daily doses of a total of 10 g of ascorbic acid were administered to healthy human subjects. Daily urinary samples of these subjects were collected before and during the treatment, and calcium contents of these samples were measured. Among the 22 subjects, 19 experienced no significant changes in urinary calcium levels during the ingestion of ascorbic acid, one subject experienced an increase, two had a decline. These changes in urinary calcium levels were relatively small and were within the changes from consuming normal diets. In the second experiment, urinary samples of 46 healthy subjects were collected during a period of 8 hours after the ingestion of 2 g of ascorbic acid (33 times the U.S. RDA). A significant increase in mean urinary calcium excretion from 48.2 +/- 25.1 mg to 58.3 +/- 28.0 mg in the 8-h time period was observed. Mean urinary volume and phosphorus were unchanged. Calcium levels of the initially low excretors were significantly elevated while the change in urinary calcium levels of the initially high excretors was not statistically significant following the administration of ascorbic acid. The results suggest that ascorbic acid has a short-term effect on the regulation of the absorption and metabolism of calcium in humans.