To investigate the effectiveness of bispectral index (BIS) during intravenous anesthesia with remifentanil and propofol in children. Forty ASAI or II pediatric patients undergoing selective surgery were divided into 4 equal groups according to age: Group A (< or = 3 m), Group B (> 3 m - 2 y), Group C (2 - 6 y), and Group D (6 - 12 y). In all groups, anesthesia was induced with remifentanil 1 microg/kg and propofol 3 mg/kg, maintained with remifentanil 0.25 microg . kg(-1) . min(-1) and propofol 6 mg/kg(-1) . h(-1). Scores of BIS and University of Michigan sedation scale (UMSS) were recorded before induction (T(1)), after induction (T(2)), at intubation (T(3)), at skin incision (T(4)), at stopping of anesthetics (T(5)), at spontaneous respiration (T(6)), and at extubation (T(7)). The time between stopping anesthetics and spontaneous respiration and the time of extubation were recorded respectively. (1) The BIS values at T(2), T(3), T(4), T(5), and T(6) were lower compared with that at T(1) in all groups (all P < 0.01). (2) There was no significant difference in the spontaneous respiration recovery time among all groups. The extubation time of Group A was much longer than those of Groups B, C, and D (all P < 0.01). (3) The UMSS scores at T(1) and T(7) in all groups were all lower than those at T(3). BIS effectively monitors the depth of intravenous anesthesia with remifentanil and propofol.