Ten patients with obstructive sleep apnoea syndrome cured by uvulopalatopharyngoplasty were compared to nine patients considered as surgical failures, using cardiovascular reflex tests--Valsalva manoeuvre, respiratory sinus arrhythmia, isometric handgrip and head-up tilt. Two patients had signs of moderate vagal dysfunction, but no case of definite autonomic nervous dysfunction was diagnosed. The overall results indicated sympathetic overreactivity, positively correlated to oxygen desaturation indices and remaining after successful treatment. Four patients did not exhibit bradycardia during sleep apnoea. Two of them had decreased respiratory sinus arrhythmia when awake, but two had normal values. This implies a difference in vagal responsiveness between the awake and sleeping states, or that other factors besides vagus function influence the bradycardia response to apnoea. The group mean values were all within normal limits. There was no significant difference between the two groups in any test. Autonomic nervous dysfunction therefore does not seem to contribute to surgical failure, nor to occur with increased incidence among patients with primary obstructive sleep apnoea syndrome.