Introduction: A synergism exists between the combination of non-depolarizing muscle relaxants with different molecular structures i.e. steroidal and benzylisoquinolinium. Smaller amount of each drug can be used, thus lower the side effects which could happen when administered alone in higher dose.Objectives : To compare the onset, duration and hemodynamic changes including the duration of additional incremental doses of atracurium, vecuronium when given as a single agent or in combination.Methods : Eighty-nine ASA class I or II patients, aged 18-80 years, scheduled for elective abdominal surgery. They were randomly assigned to one of the three groups. All received same type of anesthetics consisting of 10 mg of diazepam orally as premedication and they were induced with morphine-thiopental. Group A (Atracurium group, n = 30) was given atracurium 0.6 mg/kg, group V (Vecuronium, n = 30) received vecuronium 0.15 mg/kg and group C (Combined, n = 29) received vecuronium 0.05 mg/kg and atracurium 0.2 mg/kg. Anesthesia was maintained with N2O in O2 and additional morphine 1-2 mg. as needed. Neuromuscular blockade response was monitored by adductor pollicis acceleromyography. The speed of onset of neuromuscular blockade was determined when a TOF response = 0. Additional muscle relaxant equals to? pf the omotoa; dpse was given when TOF response = 2 or T1 recovery twitch height was > 10% which will determine the duration of initial and additional doses. Noninvasive blood pressure, pulse oximetry, capnography, electrocardiography and core temperature were monitored.Results : There were no statistical differences in demographic data, baseline blood pressure and heart rate of the patients. The onset time was significantly longer in group C compared with group A and V (group C = 270.48 ± 67.43 sec, group A = 213.13 ± 61.38 sec, group V = 183.40 ± 54.49 sec). The duration of initial bolus dose was comparable between group A and C (36.11 ±9.21) min for group A and 34.78 ± 9.56 min for group C) but significantly shorter than group V (43.98 ±12.12 min). The duration of the incremental dose was significantly longer (p < 0.05) in group C and V when compared with group A (group C = 18.51 ±6.21 min, group V = 18.55±4.57 min, group A = 14.46 ± 3.38 min). There were no differences in the changes of heart rate, systolic and diastolic blood pressure after intubation in all 3 groups. The heart rate at 2, 3 and 5 minutes after injection (before intubation) was slower in group C compared with group A while group V had slower heart rate than group A only at 3 minutes after injection.Conclusion : The combination of atracurium and vecuronium in the equipotent dose ratio of 4:1 for intubation, using 1/3 of intubating dose of each drug, has no benefit over using the full intubating dose of single drug in term of time course and hemodynmic change. A significant longer onset was also noted.