The clinical value of heart rate and blood pressure variation (HRV and BPV) spectra was assessed in 11 consecutive patients with Guillain-Barre syndrome (GBS) on artificial ventilation. Their HRV and BPV spectra were compared with those from 28 control intensive care unit (ICU) patients without peripheral nerve disorders. ICU controls had low respiratory HRV during controlled ventilation. If present, it was closely related to, but smaller than BPV, suggesting baroreceptor reflex mediation. Respiratory HRV similar to that of healthy controls was observed only in ICU controls with significant spontaneous ventilation. HRV was prominent in a subgroup of GBS patients who suffered from bradycardia or sinus arrest, whereas GBS patients without episodic bradycardia only exceptionally had respiratory HRV. Interpretation of HRV during artificial ventilation cannot be extrapolated from experience with spontaneously breathing subjects. In contrast to diabetic neuropathy, not loss, but preservation of respiratory HRV was ominous in artificially ventilated GBS patients. A pattern of prominent broad respiratory HRV peaks and narrow BPV peaks occurred only in GBS and forebode sinus arrest.