It has already been known that succinylcholine has various cardiac effects such as bradyc adia. tachycardia and, eve cardiac arrest. Among these, bradycardia has most frequently been reported after a single administration of succinylcholine, intravenously in small children. To study the cardiac effects of suecinylcholine in children premedicated with atropine, we intravenously administered thiopental sodium for induction and then a single dose of succinylcholine for endotracheal intubation. The results are as follows: 1) Cardiac rates were significantly decreased for the most part after thiopental sodium administration. However there was no significant change in cardiac rate for the cases in an hypoxic state. 2) Succinylcholine administration produced a significantly increased cardiac rate in more than half the group and a slightly decreased cardiac rate in only a small number. 3) There were neither cardiac arrythmias nor cardiac arrest following succinylcholine administration.