Subjects with anorexia nervosa (AN) present a number of changes in autonomic system functions, such as thermoregulation, vascular motility, heart rate and rhythm, and blood pressure. We evaluated the changes in the autonomic control of heart rate and blood pressure after postural variation by means of the spectral analysis of R-R interval variability (HRV in 13 female subjects with AN diagnosed on the basis of diagnostic statistical manual (DSM-IV) criteria, a mean age of 25 +/- 5.8 years and a mean body mass index (BMI) of 16.9 +/- 2.6. The controls were 16 healthy female subjects with a mean age of 25 +/- 2.3 years and a normal BMI. The data were statistically evaluated by means of one-way analysis of variance or Student\'s t test. The high frequency (HF) components of the spectral analysis did not significantly change when passing from clino- to orthostatism in the AN subjects, but there were significant changes in the controls. The changes in the low frequency (LF) components were similar in both groups, but smaller in the AN subjects. However, the difference between the two series was not statistically significant. The variance in the orthostatic R-R intervals recorded in the AN subjects was significantly less than the clinostatic intervals, the intervals recorded in the controls. These results indicate that AN subjects show signs of autonomic dysfunction. The increase in the HF component of the spectral analysis suggests that parasympathetic modulation is abnormally persistent during orthostatism, furthermore, the variability of the R-R intervals indicates that orthosympathetic regulation is also altered in AN.