Blood pressures and heart rates were recorded with Twin-Viso (Sanborn, USA) for comparative estimations of cardiovascular responses by injection of intravenous anesthetic agents-2.5% solution of Pentothal Sodium (Abbott Laboratory, USA) and Thiotal (Samsung Pharmaceutical Co., ROK) mongrel dogs. Dogs were evaluated the hepatic function by biochemical studies of blood such as total protein, albumin, total bilirubin, direct bilirubin, thymol turbidity test, alkaline phosphatase, serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGOT). Liver biopsies were performed in dogs for identifications of hepatic darnages by injection of the above barbiturates, The following results were observed: 1) It was observed the remarkable negative inotropic effect in myocardium of the mongrel dogs intravenously injected with 20 mg/kg of the above barbiturates for three minutes (Table 7, Fig. 8) 2) It was noted slight negative inotropic effect in mongrel dogs intravenously injected with 10 mg/ kg of the above barbiturates for thirty seconds (Table 8, Fig. 8). 3) It was more shorter recovery time from negative inotropic effects in mongrel dogs injected with Thiotal than in the dogs injected with Pentothal Sodium. 4) It was noted no significant changes in pathological studies of Hematoxylin-Eosin stained liver specimen and liver function studies of the blood by biochemical analysis in mongrel dogs intravenously injected everyday with 10 mg/kg of the above barbiturates. 5) It was noted slight changes in mongrel dogs injected with 20 mg/kg of the above barbiturates on TTT, Alkaline Phosphatase, SGOT and SGPT as biochemical analysis in comparing with controI values. These values, however, were not concided with the pathological findings of HematoxyIin-Eosin stained liver biopsy specimen. The facts explain to be inquired into further investigations in the pathological and biochemical aspect.