In rats, the intravenous infusion with acebutolol lead to a dose dependent decrease of arterial blood pressure, heart rate, cardiac output and total peripheral resistance, to sinus bradycardia, widening of the QRS complex, 1st and 2nd degree AV-block and intraventricular conductance disturbances. Nine possible antidotes were administered i.v. to rats which had been infused with 2 mg/kg X min acebutolol for 60 min. Isoprenaline proved the best antidote against acebutolol antagonizing the bradycardia by 88% and the hypotension completely. The activities of orciprenaline and prenalterol were lower than those of isoprenaline. Dopamine, epinephrine and norepinephrine antagonized acebutolol-induced hypotension, but did not influence considerably the bradycardia. Glucagon, on the other hand, antagonized the acebutolol-induced bradycardia by 47% but exerted only a small activity on the hypotension. Aminophyllin and calcium were nearly ineffective as antidotes against acebutolol. Isoprenaline and dopamine infused simultaneously restored heart rate, arterial blood pressure and cardiac output of acebutol-poisoned rats. The survival time of rats infused with 4 mg/kg X min acebutolol was doubled by the additional infusion of 0.2 mg/kg X min isoprenaline. The antagonistic activity of a treatment with isoprenaline and dopamine against the cardiovascular toxicity of acebutolol was confirmed in rabbits.