BACKGROUND: The purpose of this study was to assess the optimal time interval between rocuronium pretreatment and succinylcholine for prevention of the rise in serum potassium and creatine kinase concentrations and the increased incidence of fasciculations and myalgia following succinylcholine administration. METHODS: We have studied 60 patients undergoing a minor elective surgery, in a prospective double blinded method. Three groups of 20 patients each were pretreated with saline 2 ml (Group C), 0.05 mg/kg rocuronium one min before (Group R1) or 3 min before (Group R3) 1.5 mg/kg succinylcholine administration. Serum potassium and creatine kinase were respectively measured 5 min after succinylcholine and 24 h after the operation. Fasciculations and myalgia on postoperative day 1 and day 2 were evaluated. RESULTS: The increase in the serum potassium concentration was not attenuated in any group. The increase in creatine kinase concentration, the incidence of fasciculations and the incidence of myalgia on postoperative day 1 and day 2 were highest in Group C; however, there was no difference between the Group R1 and R3. CONCLUSIONS: Either a 1 min or 3 min pretreatment time interval of the rocuronium has a similar effect on the prevention of the rise in serum potassium and creatine kinase concentrations and an increased incidence of fasciculations and myalgia following succinylcholine administration.