The author explains the mechanisms of insulin resistance and impaired insulin secretion which are the main signs in the pathogenesis of non-insulin-dependent diabetics. Both reasons are the basis of secondary failure of sulphonylurea treatment or the necessity to administer large doses of insulin to achieve a normal blood sugar level in these patients. By combined treatment, i.e. by adding small amounts of insulin to the original treatment with sulphonylurea antidiabetics or by adding sulphonylurea to large insulin doses, it is possible to compensate the patient as effectively as with insulin treatment alone. The author analyzes the procedure of changing over to combined treatment which should be implemented during hospitalization of the patient. Finally the author evaluates the effect of combined treatment from data in the literature as well as his own experience which indicate that to achieve equal metabolic compensation combined treatment with sulphonylurea and insulin requires substantially lower insulin doses, as compared with insulin treatment only.