Intracerebroventricular administration of BaCl2 was found to produce severe, fatal convulsions in male Swiss-Webster mice with an LD50 (95% C.L.) at 10 min postadministration of 0.597 (0.395–0.901) ?mol/mouse. Antagonism of BaCl2-induced convulsions and lethality was obtained with pretreatment of atropine (1 to 5 mg/kg, ip) or naloxone (1 to 5 mg/kg, sc). A multivariate logistic model was used to examine the effect of atropine and naloxone on BaCl2 lethality. Atropine was found to be significantly more efficacious than naloxone in antagonizing BaCl2 lethality.