The lower oesophageal sphincter (LES) is the main barrier against gastro-oesophageal reflux. Various anaesthetic drugs have been reported to affect the LES pressure. In this study, the effects of cisapride, atropine, suxamethonium, vecuronium and pancuronium on the LES pressure of six mongrel dogs anaesthetized with propofol and nitrous oxide were investigated. By means of eight-channel pressure profilometry the LES pressure was measured in consecutive sessions before and after administration of each drug. Compared to basal values, atropine and suxamethonium significantly decreased LES pressure, pressure vector volume and sphincter length. Cisapride significantly increased all sphincter parameters, vecuronium significantly increased LES pressure and pressure vector volume while pancuronium had no significant effects. A significant decrease of the LES pressure and pressure vector volume was observed when nitrous oxide was omitted from the ventilation mixture. Three-dimensional imaging showed an asymmetric shape of the LES pressure which resulted from radial differences of the LES pressure. The results from this study show that both the anaesthetic animal model and the eight-channel pressure profilometry are useful procedures in studying the effects on sphincter function of different drugs during anaesthesia.