The heart rate response to deep breathing (DB test) and standing (30:15 r test) and the blood pressure response to standing (LS test) and sustained handgrip (HG test) were assessed in 19 obese subjects and 15 age matched lean controls. The results of DB, 30:15 r and LS tests were not significantly different in both groups. The diastolic blood pressure increase during handgrip was significantly higher in obese than in control subjects. After a period of caloric restriction the tests were repeated in 9 patients who had obtained a weight loss of at least 5 kg: a significant decrease in heart rate, diastolic blood pressure and 30:15 r results was observed, whereas the caloric restriction did not cause significant variations in the results of DB, LS and HG tests. Our results suggest that in obese patients some autonomic nervous changes can occur before and after weight loss.