1. Studies of the effect of the local injection of insulin on vitamin C metabolism in the tissues of the forearm and the buffy layer have been carried out in eight normal and eight diabetic subjects. The range of plasma and buffy layer concentrations of vitamin C were wide and overlapped in the two groups.
2. In the fasting state there was an output of vitamin C from the peripheral tissues in both groups and this was increased in the non-diabetics after insulin, whereas the response in the diabetic subjects was variable.
3. It is concluded that insulin influences vitamin C metabolism in the peripheral tissues in man, and that the response is abnormal in many diabetic subjects.