Thiazide treatment is a first-line choice for hypersensitive patients: Thiazides have a flat dose-response as regards blood pressure, but induce biochemical changes only at higher doses. Given in low doses, which careful monitoring of potassium, thiazides provide adequate control of blood pressure without having any substantial impact on blood glucose. In high doses, thiazides may induce three to six new cases of impaired glucose tolerance per 1,000 patient years. The thiazide-induced changes in blood glucose can be prevented by giving lower doses and correcting hypokalaemia, and can be reversed by stopping the drug. In most diabetics, low doses of thiazides do not seem to diminish control of blood glucose. The well-documented effect of thiazides in reducing cardiovascular morbidity and mortality, their safety and their low price make them an excellent first-line choice for treatment of hypertension.