This study was designed to evaluate the safety and efficacy of the new domestic product, Citosol(R) (thiamylal sodium) as an intravenous induction agent, by comparing with the most popularly used thiopental sodium in modern clinical anesthetic practice, and also to observe if there is any more harmful effect than thiopental sodium on the hemodynamic status of the patient. 60 patients who admitted to Seoul National University Hospital to receive operations at departments of E.N.T., Gynecology, and Ophthalmology, with ASA physical status 1 or 2, were randomly assigned to be given either thiamylal sodium, 3.4 mg/kg (n=30), or thiopental sodium, 5 mg/kg (n=30), intravenously, for induction, While administering 100% oxygen, patients were given vecuronium, 1,5 mg/kg, i.v., and intubated at the end of three minutes after administration of vecuronium. After intubation, anesthesia was maintained with 50% N2O. O2 and isoflurane. Both thiopental sodium and thiamylal sodium produced significant decrease in arterial pressure without significant increase in heart rate during mduction period. No disastrous complications were seen during the induction period with the use of either drug. Also there was no significant difference between two groups in the incidence of complications or in the changes of arterial pressure and heart rate except a statistically significant greater ineidence of pain on injection with the use of thiopental sodium. Above results suggest that thiamylal sodium and thiopental sodium are almost identical in their clinical actions and are both safe, and effective for use in the induction of patients but thiamylal sodium seems to have somewhat higher potency than thiopental sodium, and brings less pain during intravenous injection, which enables the induction more comfortable.