Aim: Glitazones are powerful insulin sensitizers prescribed for the treatment of type 2 diabetes. Their use is however associated with fluid retention and an increased risk of congestive heart failure. We previously demonstrated that pioglitazone increases proximal sodium reabsorption in healthy volunteers. This study examines the effects of pioglitazone on renal sodium handling in subjects prone to insulin resistance, i.e. diabetic and/or hypertensive subjects.