The variations of plasmatic beta-endorphin and cortisol levels are studied in 3 groups of patients. These subjects are submitted to abdominal surgery following 3 different anaesthetic schemes: neuroleptanalgesia (droperidol and fentanyl), pure analgesia (fentanyl), association halothane - small dose of fentanyl. The study covers the period from premedication through recovery. The results of this work demonstrates that the average level of beta-endorphin in neuroleptanalgesia and pure analgesia series is stable; there is an increase in the halothane series just after the incision until waking up. The average level of cortisol is stable for the 3 series until incision. It is strongly increased in the neuroleptanalgesia series and in the halothane series. This increase is delayed and reduced in the fentanyl series.