First degree relatives of patients with non-insulin-dependent diabetes mellitus (NIDDM) have a 40% risk of developing NIDDM during their lifetime and the risk seems to be greater if the disease is inherited from the mother than from the father. It has also become clear that metabolic abnormalities are demonstrable long before the disease becomes manifest. The prediabetic state is associated with a predisposition to abdominal obesity, insulin resistance, lipid disorders, high blood pressure, and microalbuminuria, ie, the metabolic or insulin resistance syndrome. It is, however, not yet known whether treatment of these abnormalities is able to prevent progression to manifest NIDDM.