Teflurane was first used in man in 1960. A series of thirty anesthetics completed in the first six months suggested that the teflurane was essentially non-toxic to the circulatory system and to hepatic and renal function. However, when the drug was given at inspired concentrations of 10 % and above, cardiac arrhythmias appeared, increased in severity and significance and systolic and diastolic blood pressures fell in direct proportion to the concentration given. That is why the further development of the teflurane was terminated.