BACKGROUND: Although the pro-convulsant or anticonvulsant properties of propofol remain a matter of controversy, it is evident that propofol can produce involuntary movement. Such movement is a relatively common side effect, especially in children, and may be dose-related or injection rate-related. The goal of this study was to evaluate the effect of injection rate upon involuntary movement during propofol induction in children. METHODS: Children (age 3-14 yr) undergoing elective Eye and ENT surgery were randomly allocated to one of 4 groups based on the propofol injection rate (A, manual/15 s; B, 360 ml/hr; C, 200 ml/hr, D, 100 ml/hr) using a manual injection method and syringe pumps. No premedication was used. The induction dosage of propofol was 3 mg/kg in all groups. Fentanyl 1mcg/kg and 1% lidocaine 1-2ml were given I.V. before propofol. Involuntary movement was graded 0-2 on severity. The infused dose of propofol at movement was measured. Movement due to pain or mask fitting was not regarded as an involuntary movement. All results were analyzed using the Chi-Square Test and ANOVA. RESULTS: 595 children were studied. Age, gender, and weight were similar in the 4 groups. Involuntary movements were apparent in 179 (30.1%) of the 595 subjects. Movements were significantly less in group A (12.4%) and B (16.4%) compared to group C (46.6%) and D (45.3%). The grades of movement were not different among the 4 groups. The durations of movement in group A and B were significantly short compared to group C and D. The infused dose of propofol (mg/kg) at movement was higher in group C (2.65+/-0.62) than in A (1.99+/-0.62) and B (2.43+/-0.78). There were no significant hemodynamic and SPO2 changes during and after the propofol injection. CONCLUSIONS: We concluded that slow injection may increase the incidence of involuntary movement during propofol induction in children. Since the bolus injection rates are usually slow in most syringe pumps, manual injection for 10 15 s may be a better choice for smoother induction, as it requires fewer interventions to prevent venous catheter displacement in children.