SUMMARYCirculatory responses to the intravenous injection of accelerating doses of atropine sulphate were studied in ten patients anaesthetized with nitrous oxide, oxygen and gallamine triethiodide and ventilated artificially. Small but significant increases in heart rate and cardiac output were accompanied by lowering of total peripheral resistance and circulation time. Arterial pressures, stroke volumes and stroke work were unchanged. Initial heart rates and pressures were high, due to the use of gallamine, and it is suggested that the control levels of cardiac output were also high. This would account for the smaller changes seen compared with earlier reports of the effect of atropine in patients artificially ventilated using tubocurarine and in those spontaneously breathing nitrous oxide, oxygen and halothane.