Epinephrine is routinely used as a marker for intravascular injection during administration of regional anesthesia. The cardiovascular response of patients on beta-blockers to such a test dose has been reported to be unpredictable. We investigated this interaction by administering 15 µg of epinephrine intravenously to 6 healthy volunteers 39 to 48 years old before and after beta-blockade, accomplished by intravenous injection of propranolol, 0.04 mg/kg. Epinephrine administration caused a 20 ± 4% (mean ± SEM) increase in heart rate before beta-blockade but a 38 ± 3% reduction after beta-blockade. The lowest heart rate recorded was 28 beats/min. We conclude that, in middle-aged beta-blocked men, intravenous injection of a standard epinephrine-containing test dose will predictably cause significant hypertension followed by marked bradycardia.