Cardiac autonomic function was studied in 23 alcohol dependent men by standard tests of autonomic function and measurement of 24 hour heart rate variability. In all there was peripheral or central nervous system damage or both. Standard tests of autonomic function showed vagal neuropathy in seven. The remainder had normal autonomic function tests. Twenty four hour heart rate variability was measured as the standard deviation of the successive differences between RR intervals from an ambulatory electrocardiogram recording. Twenty four hour heart rate variability was significantly lower in both alcohol dependent groups than in controls, but the results in the two alcohol dependent groups were not significantly different from each other. The results of standard tests of autonomic function did not distinguish between the alcohol dependent men with normal autonomic function and controls. The differences in heart rate variability between this group and the controls may have been the result of the ability of this method to detect small changes in autonomic integrity. Cardiomyopathy may also account for some of these differences and such abnormalities should be excluded before results are to be regarded as a reflection of vagal function. Twenty four hour measurement of heart rate variability may be a more useful index of cardiac vagal neuropathy than currently available tests of autonomic function.