It is known from clinical observations, theoretical investigations as well as from data patients with intensified insulin therapy and wearers of insulin pumps that the body also requires insulin under fasting conditions. Therapeutic studies as well as the investigations carried out using the artificial pancreas indicate that just under half of the daily insulin requirement is not meal-related, and the other half is dependent on food. The question arose as to whether there are any differences in the basal insulin requirement depending on the time of day and whether differences can be detected between type I diabetics and healthy reference subjects. The results show that analogous changes occur in the early hours of the morning in type I diabetics and healthy normal subjects: these correspond to the clinical familiar dawn phenomenon. The different courses of blood glucose and insulin requirement as measured on the basis of the release of insulin by the Biostator as well as the insulin secretion profile in healthy normal volunteers under fasting conditions do not show any further differences which depend on the time of day.