This article reviews the effects of diet and exercise on insulin sensitivity in patients with type II diabetes (non-insulin-dependent diabetes mellitus, NIDDM). Dietary caloric restriction operative through weight loss decrease the insulin resistance characteristic of the disease by increased glucose transport. The precise localization of this effect is unknown, as is the defect in the insulin signalling pathway in type II diabetes. Inherent problems are the inability to clearly separate obesity and type II diabetes and methodological difficulties in the distinction of dietary effects from exercise-induced effects. The mechanism of exercise-induced insulin sensitivity has gained considerable understanding through the detection of the glucose transporter molecule GLUT-4 in muscle. It is now clear that the presence of insulin is not mandatory and mere electrical stimulation of the muscle produces similar effects through distinct signalling pathways. Exercise-induced increased blood flow and decreased vascular resistance may also play an important role. In contrast to these newer experimental data, clinical studies and feasibility studies aimed to implement exercise as a valuable therapeutic measure in type II diabetes have failed to delineate promising long-lasting effects and can therefore not be generally recommended. Encouraging epidemiological data have recently been found with respect to the prevention of type II diabetes by increased physical activity in patients at risk.