1. Blood pressure, heart rate and cardiac output were measured in six rabbits before, during and immediately after treadmill exercise. During the same periods the dynamic gain of the carotid-sinus baroreceptor reflex was estimated by creating a sinusoidal oscillation of carotid-distending pressure.

2. The average blood pressure did not change significantly during or after exercise, but heart rate and cardiac output rose markedly and there was a concomitant fall in systemic vascular resistance.

3. The reflex gain for blood pressure decreased by one-fifth during exercise, and the gains for heart rate and vascular resistance by two-fifths. Immediately after exercise the gains for all three variables decreased further, to between one-half and one-third of the resting values.

4. Our results indicate that during and after dynamic exercise the correction of a potential disturbance of blood pressure by the carotid-sinus baroreceptor reflex is decreased in magnitude or in speed.

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