1. Plasma adrenaline was measured at rest and on exercise in six normal, non-atopic subjects. The exercise test produced a minimum tachycardia of 158 beats/min and a mean plasma adrenaline level of 1.89 nmol/l.
2. On a separate occasion, two doses of l-adrenaline (0.025 μg min−1 kg−1 and 0.05 μg min−1 kg−1) were infused in the same subjects at rest to produce two mean plasma levels similar to those found on exercise.
3. Significant bronchodilation and elevation of plasma glucose occurred with both infusion doses when compared with placebo.
4. Neither infusion caused a significant change in heart rate and only the higher dose caused a small but significant rise in systolic and fall in diastolic blood pressure.
5. Our results suggest that adrenaline as a hormone, at the levels found on exercise, is capable of causing bronchodilation and glycogenolysis in normal subjects. Its contribution to the cardiovascular response to exercise appears to be slight and suggests that its role in cardiovascular physiology may also be marginal.