A mixture of fluam'son, 10 mg/ml and fentanyl, 0.2 mg/ml, commercially available as Hypnorm® has been used in rats. Judged by the practical experience over five years it seems that this combination offers an anaesthesia which in certain respects 2'5 superior to that of barbiturates in the rat. It is faster, depresses less autonomic reflexes and there seems to be fewer complications both during and after the anesthesia. The most serious unwanted effect is depression of respiration, but it was only observed at high doses.