Insulin is a peptide comprising of two peptide chains (A and B) linked by S-S bonds. Insulin secretion is stimulated primarily by hyperglycaemia and with amino acids. Other hormones such as glucagon, and neural stimuli are also contributing. Insulin is one of the key hormones with regard to metabolism. . Its determination is useful in the ddiagnosis of insulinoma and other hypoglycemic states. In diabetic states, it is determined rather for therapeutic decision than for diagnosis of diabetes itself.