8 healthy subjects were infused with arginine at h. 08 and h. 16 of different days in order to observe if some changes occurred in the biphasic insulin response according with the different times of the day. A statistical difference between the two responses could be observed only for the first phase of the insulin response (time 0' - 10'), that appeared greater in the morning. When the insulin areas were plotted against the percentage of Ideal Body Weight an highly statistically significant correlation was found.