Direct arterial pressure(DAP) and heart rate were observed in normal patients during and after intravenous injection of d-Tc at varying rates of administration. The injection of d-Tc was preceeded by antihistmine(hydroxysine) in group ll. The results were as follows: 1) Alteration of pulse rate was minimal following varied administration of d-Tc in all groups. 2) DAP showed maximal change following a bolus injection of d-Tc, and a minimal change at the end of 180 seconds of d-Tc administration. 3) DAP showed minimal change following the premediction with antihistamine in comparison to a bolus administration. 4) Manifestation of flushing and tachycardia due to histmine release were not observed in group l and group ll.