Cyclic AMP, glucose and Cortisol in plasma were measured before, during and after major surgery (hysterectomy, six patients) and minor surgery (tympanoplasty, 10 patients). During major surgery cyclic AMP as well as glucose and Cortisol showed a pronounced increase. During minor surgery cyclic AMP, glucose and Cortisol levels were significantly lower than in the group undergoing major surgery. It is concluded that the increase of plasma cyclic AMP during operative procedures is related to the severity of the trauma.