The effects of total intravenous anaesthesia with an intravenous infusion of a combination of guaiphenesin, ketamine and detomidine were studied in 10 patients scheduled for elective surgery. Anaesthesia was maintained by the infusion of guaiphenesin (100 mg/ml), ketamine (2 mg/ml) and detomidine (0.02 mg/ml). The infusion rate was 1 ml/kg/hr. During anaesthesia, pulse rate and mean arterial blood pressure were continuously recorded. Arterial blood gases and pH were determined immediately after induction and at stated times during anaesthesia. Venous blood was sampled to determine plasma glucose, lactate, lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and aspartate aminotransferase (AST) concentrations. Values were compared with those determined in blood sampled before the premedication. All determined parameters with the exception of the plasma glucose concentration, the arterial oxygen tension and the AST concentration did not change significantly and remained within normal ranges. The plasma glucose concentration increased significantly after the induction of anaesthesia compared to the control value but decreased to normal values during anaesthesia. The arterial oxygen tension was on average 30% lower than normally wished. Compared to the control value the plasma concentration of AST was significantly decreased at the end of anaesthesia. Based upon the results of this study an infusion of guaiphenesin, ketamine and detomidine appears to be useful for the maintenance of total anaesthesia in horses.