The effects of methscopolamine bromide (MSB) and atropine were compared in patients prior to elective surgery. After administration of the second dose of MSB (total dose 1.5 mug/kg) all patients exhibited at least 20% increase in heart rate. In contrast, three doses of atropine (total dose 5.3 mug/kg) were required for most patients to attain a 20% increase in heart rate while 2 patients did not attain this heart rate with a dose of 10.6 mug/kg of atropine. Comparison if single injections of MSB and atropine in normal subjects also demonstrated a more reliable dose-response relationship with MSB. Electrocardiographic changes recorded were typical of those reported with anticholinergic agents. Sinus and atrial arrhythmias were more common with atropine and nodal arrhythmias and conduction disturbances were more common with MSB. This study demonstrated that MSB can be reliably substituted for atropine when an anticholinergic drug is needed to increase heart rate. Since MSB has a limited ability to cross the blood-brain barrier, it may be the more desirable drug in patients in whom the central nervous system effects of atropine may be deleterious.