The influence of the daily ingestion of 1, 2, 3, and 5 grams of ascorbic acid on whole blood and plasma ascorbic acid levels and on the urinary excretion of ascorbic acid has been investigated. The ingestion of one gram of ascorbic acid per day for one week significantly increases plasma and whole blood levels over presupplementation levels, but larger amounts of ascorbic acid do not further increase plasma and whole blood ascorbic acid levels. Urinary excretion increases with intake, up to intakes of 3 grams per day but does not increase further when 5 grams of ascorbic acid is ingested per day. Upon discontinuing ascorbic acid supplementation the plasma and whole blood levels decline rapidly and the urinary excretion of ascorbic acid falls to presupplementation values within a few days. The results suggest that there is need for a detailed study of the routes of excretion of ascorbic acid at high levels of intake and that the safety of ingesting large quantities of ascorbic acid may be questioned.