Abstract: A therapeutically effective amount of L-arginine, or a physiologically acceptable salt thereof, is orally administered, preferably as a food supplement in combination with a meal approved by the American Diabetes Association Inc. ("ADA"), to a person having Type II diabetes mellitus but who is not on either insulin or other medication for glycemic control. When 3 g to 15 g of L-arginine is ingested concurrently with a meal, or immediately prior to eating a meal, the L-arginine decreases the concentration of insulin generated, compared to that generated after the same meal without the L-arginine; at the same time, concentration of glucose in the person's blood is decreased, indicating that available insulin sensitizes cells so as to nearly mimic the effectiveness of normal cells in a non-diabetic person; from 3 g to 15 g of orally ingested L-arginine, by itself, produces no measurable increase in insulin secretion in a diabetic.