Previous studies have shown that an elevated basal metabolic rate (BMR) is present in elderly malnourished cancer patients. A possible dysfunction of the autonomic nervous system needs to be demonstrated. In aged weight-losing cancer patients (n = 40), aged non-weight-losing cancer patients (n = 30), and aged weight-losing noncancer patients (n = 18), the baseline BMR and heart rate variability were studied. Aged weight-losing cancer patients (n = 40) underwent bioimpedance analysis, ambulatory electrocardiographic monitoring with analysis of heart rate variability, and determination of the BMR. Then, the patients received infusion of Intralipid (Pharmacia, Uppsala, Sweden) without and with propranolol (6 days of 40 mg twice daily) administration. At baseline, a simple correlation between the BMR and the low-frequency component (LF) (r = .42, P < .006) and LF to high-frequency (HF) ratio (r = .51, P < .001) was found. After propranolol administration, the percent decline in the BMR was significantly correlated with the percent decline in the LF (r = .39, P < .01) and LF/HF ratio (r = .53, P < .001). The percent decline in the BMR was not correlated with the HF (r = .13, P < .34) or the plasma noradrenaline concentration (r = .21, P < .20) at any time. With regard to the BMR and substrate oxidation, 6-day propranolol administration plus Intralipid infusion produced the strongest decline in the BMR. This study demonstrates that autonomic nervous system dysfunction occurs and is responsible for the elevated BMR in elderly cancer patients, propranolol administration rectifies the autonomic dysfunction, and Intralipid infusion combined with propranolol administration is useful for enhancing the daily caloric intake without a strong increase in energy expenditure.