Videoendoscopy of the oropharynx was performed in 57 patients with habitual snoring and obstructive sleep apnoea syndrome. Endoscopy was done in waking supine subjects relaxed and during voluntary snoring, Esmarch's and modified Müller's manoeuvre. Evaluation of results for the first time was semiquantitative. Statistical analysis showed significant correlations (p less than 0.004) between movements of the base of the tongue and the modified Müller's manoeuvre. For the first time it could be shown that the dynamic changes in the pharyngeal walls during voluntary snoring are identical with those in the modified Müller's manoeuvre (p less than 0.006). Frame-by-frame analysis demonstrated epiglottic movements in the inspiratory cycle of snoring which result in a massive occlusion of the airway in 65% of our patients. Videoendoscopy is able to provide valuable information on anatomical details and potential obstructive sites but cannot predict the success of surgical interventions like UPPP. Videoendoscopy due to its high resolution in the time domain can demonstrate pathophysiological events which are otherwise inaccessible. For the experienced examiner videoendoscopy is a fast tool for obtaining live information on the surgical site.