For the practical implementation of every type of insulin therapy it is necessary to know both the time course of action of therapeutically used short- and long-acting insulin preparations and the factors influencing such time-action profiles. The only reliable way to obtain the required quantitative information about the pharmacokinetic and glucodynamic properties of insulin preparations has been the use of the euglycemic glucose clamp technique. The first studies with each new insulin formulation or insulin application technique should be performed with healthy subjects in order to have the most comparable study conditions. Thereafter, results from such clinical-experimental studies should be verified in similar studies with patients with diabetes. Earlier investigational approaches, which either had been limited to the determination of the pharmacokinetic properties of insulin preparations or had used the quantitative decrease of the blood glucose level as a measure of the pharmacodynamic properties, do not provide valid quantitative results. The proposed glucose clamp technique makes possible the quantitative study of the pharmacokinetic and pharmacodynamic properties of insulin preparations under comparative and reproducible conditions.