When either a 960-kcal, 140-g carbohydrate meal, or a 75-g glucose load was ingested by non-diabetic Caucasians, the 2-h venous plasma glucose concentration was higher by 0.82 and 1.25 mmol/l, respectively, if the ambient temperature was 33 degrees C rather than 23 degrees C. It is likely that this is a result of relative 'arterialisation' of the venous blood. Even at 23 degrees C room temperature, use of the 'hot hand' technique to obtain 'arterialized' venous blood increases post-load glucose levels in contralateral antecubital veins. If these observations apply to those acclimatised to the heat, they could affect the diagnosis of both diabetes and impaired glucose tolerance in the tropics.