In the case of a conscious man suffering from a painful injury in the facial and trigeminal nerves, the administration of intra-muscular injections of increasing doses of morphine and sulfentanil provokes constant analgesia in direct proportion to the administered dose. The admitted dosages for each product are as follows. M = 0,100, 0,150, 0,200 mg/kg S = 0,00015, 0,0003, 0,0006 mg/kg. Sulfentanil is a highly active analgesic whose activity is about 333 times greater than that of morphine and 13 times greater than that of fentanyl. In the case of each of the 3 products, the point at which analgesia becomes clinically discernable is the same. Optimum intensity of action of the analgesia is arrived at in all 3 cases within a period of 60 to 90 minutes. The higher the dose administered, the longer sulfentanil can be expected to work. Although effective for a shorter period of time than morphine and fentanyl sulfentanil effectiveness is too great for it to be considered a short-acting analgesic.