BACKGROUND: To reduce side effects (hyperlipidemia, pain on injection, etc.) of the present formation of propofol, many attempts to change the emulsifying agent for propofol have been tried. This study was designed to examine the poloxamer-407 as an emulsifying agent for propofol compared to soybean oil regarding histamine release and plasma lipid levels. METHODS: Twelve Beagle dogs weighing 12 - 16 kg were randomly assigned to one of two groups according to the formulation of propofol. Group 1 received Diprivan propofol 1% (AstraZeneca Co. UK), and group 2 received poloxamer-407 formulated propofol by a continuous intravenous infusion at 30 mg/kg/h for 3 hours. Three, 6, 9 and 12 hours after discontinuing the propofol infusion, venous blood samples from the cranial tibial vein were analysed by an ELISA kit for the histamine level. Also, blood lipid levels were checked 3 hours after the infusion and blood propofol concentration were checked every hour during the infusion. RESULTS: Group 2 showed significantly less histamine release than group 1 at 3, 6 and 9 hours after the infusion (P < 0.05). In the plasma lipid study, there was no difference in high-density lipoprotein (HDL) between the two groups, but triglyceride and cholesterol were significantly higher in group 2 (P < 0.05). There was no difference in propofol concentrations between the two groups. CONCLUSIONS: Poloxamer-407 as an emulsifying agent for propofol showed no advantage compared to a present formulation regarding hyperlipidemia, and even decreased the histamine level.