Intravenous succinylcholine is often associated with adverse effects, including muscle fasciculation, postoperative myalgia, increased intraocular and intragastric pressure, along with potassium and creatinine phosphokinase, myoglobinuria, and disturbances in cardiac rate and rhythm. Several methods have been used to modify these side effects, the most popular of which has been the of subparalyzing doses of nondepolarizining relaxants prior to injection of succinylcholine. With such pretreatment however satisfactory muscular relaxation is often not achieve, necessitaing use of larger doses of succinylcholine becauses pretreatment renders the endplateless sensitive to succinylcholine; hence large doses of succinylcholine are necessary to ensure adquate degress of relaxation. The present investigation was undertaken to determine the effects of flunitrazepam on the adverse effects of succinylcholine. This paper covers the period from March, 1981 to March, 1982 in the Department of Anesthesiology, Hanyang University Hospital. The 45 subjects were divided into 3 groups: 1) propanidid (8mg/kg) with succinylcholine 2) flunitrazepam(0.03mg/kg) with succinylcholine 3) flunitrazepam(0.06mg/kg) with succinylcholine. None had existing neuromuscular disease nor were any patients receiving diazepam or any drug known to influence myoneural blocking agent. Patients with burns, muscle injury of muscle atrophy were excluded. In each group, the plasma concentration of potassium and creatinie phosphokinase was observed before and 10 minutes after use of succinylcholine. Also succinylcholine in duced myalgia, fasciculation, onset of loss of eyelid reflex and relaxation were observed and compared. The conclusions are as follows: 1) There were no significant changes of plasma concentration of potassium and creatinine phosphokinase in presuccinylcholine and 10 minutes postsuccinylcholine. Also any statistically significant changes were not observed in the comparison of the propanidid group and the flunitrazepam groups. 2) Flunitrazepam significantly diminished the incidence of postoperative muscle pain and it was shown that the degree of fasciculation has no relationship with succinylcholine induced muscle pain. 3) In the propanidid group, the onset of loss of eyelid reflex was most rapid(22±13 second). In the flunitrasepam 0.03mg/kg group, the onset of loss of eyelid reflex was statistically significant (p<0.05), as compared with the 0.06mg/kg group(42±27 second). 4) In all groups, excellent conditions of intubation were observed. Propanidid and flunitrazepam did not affect the magnitude nor duration of the succinylcholine neuromuscular block.