BACKGROUND: Several recent studies have suggested the context-sensitive half-time (CSHT) as a clinically more relevant measure of decreasing drug concentrations after a constant infusion of a given duration. The purpose of this study was to simulate the CSHT using a PK-SIM computer simulation program and compare this with duration of propofol infusion and real awakening time from anesthesia for the evaluation of CSHT as a useful tool of prediction of recovery from anesthesia. METHODS: Ninety-five ASA class I or II adult patients (18-55 yrs) scheduled for orthopedic elective surgery were randomly allocated into 5 groups according to duration of propofol infusion. Five groups were Group 1: less than 60 min, Group 2: 61-120 min, Group 3: 121-180 min, Group 4: 181-240 min, and Group 5: 241-300 min. Anesthesia was induced and maintained with propofol-nitrous oxide (67%)-oxygen (33%) according to Prys-Roberts' method. Propofol was discontinued immediately after skin closure and duration of infusion was checked. Duration of infusion, CSHT, and awakening time from anesthesia were compared and evaluated correlationship among them using a correlation coefficient. RESULTS: Plasma and effect site concentration after 5 hrs infusion of propofol derived from computer simulation was 3.3 microgram/ml. Awakening time for each group was 8.5-11.8 min and plasma CSHT for that was 6.4-9.5 min. The correlation coefficient (r) between duration of propofol infusion and awakening time was 0.98 (p<0.01) and that between CSHT and awakening time was 0.95 (p<0.01). CONCLUSIONS: There were strong relationship among duration of infusion of propofol, awakening time and CSHT. It seems that CSHT could be a good predictor of awakening from propofol-N20-02 general anesthesia.