AbstractAlfentanil, N‐{1‐[2‐(4‐ethyl‐4,5‐dihydro‐5‐oxo‐1H‐tetrazol‐l‐yl)ethyl]‐4‐(methoxymethyl)‐4‐piperidinyl}‐N‐phenyl propanamide monohydrochloride monohydrate, is a chemically novel, potent, extremely short‐acting and safe intravenous morphine‐like agent in laboratory animals. As an analgesic in rats, alfentanil is 137 times as potent as pethidine (tail withdrawal reaction test: i.v. ED50 is 6.04 mg/kg for pethidine and 0.044 mg/kg for alfentanil). The safety margin in rats is 1,080 (LD50: 47.5 mg/kg i.v.). Alfentanil reaches its peak effect within 2 min after injection, and its duration of action is very short: at two times its lowest ED50 the drug has a duration of action of 10 min. This duration is 30–35 min for pethidine and fentanyl, and 120 min for morphine. The narcotic antagonist naloxone produces an immediate and complete reversal of all morphine‐like effects of alfentanil. In dogs, alfentanil is a potent antiemetic (ED50: 0.032 mg/kg i.v.) with a safe