It is common to administrate neostigmiae methylsulfate and atropiae aulfate to counteract the effect of nondepolarising neuromuscular blocker. In case of cardiovascular disease, the effect of bradycardia or tachycardia resultiag from the administration of these drugs may be harmful to the patient. The purpose of this study is to investigate the effects of combinatioa and method of administration of neostigmine methylsulfate and atropine sulfate on heart rate. One hundred and two patients in both sexes were devided into three groups(A, B, C), and each group was devided into three subgroups (AI, AII, AIII, BI, BII, BIII, CI, CII, CIII). In group A, neostigmine methylsulfate and atropine aulfate were mixed and administered intravenously within fifteen seconds. In group B, atropine eulfate was administered thirty seconds after the administration of neostigmine methylsulfate. In group C, the two drugs were mixed and administered over a period of five minutes. In subgroup I the ratio of neostigmine methyliulfate to atropine sulfate was 2: 1(0. 04 mg/kg: 0.02 mg/kg) in subgroup 3 the ratio was 3: 2(0.03 mg/kg: 0. 02 mg/kg), and in subgroup lll the ratio was 1: 1(0. 02 mg/kg: 0. 02 mg/kg). The heart rate was counted just before, 0. 5 minute, 1 miaute, l. 5 minutes, 2 minutes, 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes after the administration of the drugs. The results were as follows: 1) Initial increase in heart rate was significant in lager atropine ratio. 2) The later decrease in heart rate waa less in larger atropine ratio. 3) The maximal increases in heart rate in groap A and B appeared thirty seconds apart, but there was little difference betweea them. 4) The change ia heart rate was the least in group C.