The relationship between obesity and type II diabetes mellitus is well established and a majority of type II diabetic individuals are classified as obese. The pathogenesis of type II diabetes mellitus is not fully understood; however, multiple organ systems are involved, including abnormalities of insulin secretion, peripheral insulin resistance and hepatic insulin resistance. The goal of the treatment for the obese diabetic is to normalise these alterations and achieve normoglycaemia. Traditionally, the initial therapy, aiming to accomplish weight reduction, is diet and exercise. In obese type II diabetic patients, the whole body insulin-dose response curve is markedly depressed. A single exercise session improves and partially normalises both insulin responsiveness and sensitivity for glucose utilisation. Furthermore, a single bout of physical activity often results in decreased plasma glucose levels, which persists into the postoperative period. Type II diabetes patients participating in regular exercise programmes can potentially improve their metabolic control. An improved glucose control in both lean and obese type II diabetic patients under the age of 55 years has been demonstrated by improved HbA1C levels and glucose tolerance tests following physical training programmes. The effect of regular exercise on the metabolic control in these younger patients does not appear to be correlated with weight reduction. For most type II diabetic men over 55 years of age, physical training is not a feasible form of therapy because of other interfering diseases which may complicate or severely hinder all physical training apart from very low intensity exercise programmes. Lean, older, type II diabetic patients who have been able to exercise for 10 weeks or up to 2 years demonstrate no change in HbA1C levels, glucose tolerance or bodyweight. Thus, there is a clear difference in metabolic response to regular exercise between younger and older type II diabetic patients. The younger patient appears to be more inclined to respond to physical training with improvements in the metabolic control. The reason for this apparent difference is not clear, but possible explanations may include differences in training intensity, the presence or degree of complicating diseases, pretraining level of metabolic control or bodyweight. Type II diabetics are predisposed to cardiovascular disease and are characterised by hyperlipidaemia. In obese type II diabetic individuals, physical training improves the blood lipid profile as measured by decreased levels of triglycerides and total cholesterol. In young, overweight diabetics, improved lipid profiles can be achieved despite no change in bodyweight, while no apparent effects are reported for lean patients.(ABSTRACT TRUNCATED AT 400 WORDS)