Glucose toxicity refers to the structural and functional damage in the beta cells and target tissues of insulin, caused by chronic hyperglycemia. These alterations cause a lower hormonal secretion and action (insulin resistance). Lipid toxicity refers to the damage caused by persistently high free fatty acid levels, as a consequence of triacylglycerol catabolism. Since elevated glucose and lipid levels cause a similar damage and interact, the term glucose and lipid toxicity refers to their additive effects. This toxicity can be implicated in the pathogenesis of type II diabetes and in the secondary failure of oral hypoglycemic drugs, leading to the requirement of insulin treatment. Insulin resistance with normal glucose levels, glucose intolerance and clinical diabetes are the three recognized stages in the development of type 2 diabetes. Considering that the first two stages are reversible, a good metabolic control to avoid glucose and lipid toxicity could revert or avoid the development of clinical diabetes (Rev Méd Chile 2001; 129: 671-9)