IBZM) is one of the several benzamide derivatives showing a high affinity for the central nervous system (CNS) D2 dopamine receptor. Carrier-free [123I]IBZM is potentially useful as a nuclear medicine imaging agent for investigating the CNS D2 dopamine receptor in humans. This study describes the acute toxicity of IBZM and S-N-(1-ethyl-2-pyrrolidinyl)methyl-2-hydroxy-6-methoxybenzamide (BZM) in the rats. Treated rats were administered with IBZM at dose levels of 1 and 5 μg/kg and BZM at dose levels of 250 and 1250 μg/kg with dose volumes of 1 and 5 mL/kg. The control rats were administered 5 mL/kg of vehicle control. The rats were observed for 14 days. Observations included general demeanor, clinical signs, mortality, body weights/total body weight gains, and gross necropsy findings. None of the animals died during the 14-day study period. In female rats, the body weight gained at the first week of BZM treatment at a dose level of 1250 μg/kg and the total body weight gains of both IBZM treated groups were significantly higher than the control group (p < 0.05).