Midazolam and alfentanil were infused in a totally i.v. anesthetic technique (TIVA) to patients undergoing hysterectomy. Correlations of midazolam plasma concentrations and effects were made during recovery. Due to the high doses of midazolam administered during TIVA, metabolism and not redistribution mainly governed the duration of effects post-infusion. The concomitant administration of alfentanil contributed to the sedative effect, as illustrated by a shift of the concentration-response curve to the left. As a result of these effects, recovery was prolonged and extended over 2-6 h. The effect of the benzodiazepine antagonist flumazenil on post-operative performance after total i.v. anaesthesia with midazolam and alfentanil was studied. A bolus dose of flumazenil, 1.0 mg i.v., significantly improved recovery during the first post-operative hour but was followed later by resedation. The reduction in sedation followed by improvement in ventilation, without reduction of analgesia, demonstrated that antagonism of hypnosis is the primary factor in enhancing recovery from total i.v. anaesthesia.