The new beta-blockers 4-(2-hydroxy-3-isopropyl-amino-propoxy)-carbazole (carazolol) and 1-(4-acetoxy-2,3,5-trimethylphenyloxy)-3-isopropylamino-propan-2-ol (methypranol, Disorat) were compared with 14 well-known beta-blocking agents with regard to isoproterenol antagonism (equipotent doses in the rabbit i.v.), acute toxicity (LD50 in mice i.v.) and intrinsic sympathomimetic activity (increase in the heart rate of reserpinized rats i.p.). The following descending order for the equipotent beta-receptor blocking doses was obtained: nifenalol, DCI, pronethalol, practolol, sotalol, alprenolol, bupranolol, toliprolol, propranolol, methypranol, YB 2 pindolol, bunitrolol, oxprenolol, bunolol and carazolol. Carazolol had, in addition, the highest therapeutic index and at beta-receptor blocking doses virtually no intrinsic sympathomimetic activity.