Reflex responses of mean blood pressure and of heart rate to either bilateral common carotid occlusion (CO) or unilateral carotid sinus dilatation (CSD) during rest and different behaviours have been compared in conscious cats. Unloading and loading the carotid sinus receptors elicited equal reflex responses both of mean blood pressure and of heart rate during control immobile behaviour (CO: +34 +/- 6 mmHg and +35 +/- 6 beats . min-1; CSD: -37 +/- 4 mmHg and -52 +/- 11 beats . min-1), standing on the hindlimbs (CO: +36 +/- 5 mmHg and +29 +/- 5 5 beats . min-1; CSD: -40 +/- 6 mmHg and -61 +/- 10 beats . min-1), fighting against an attacking animal (CO: +34 +/- 5 mmHg and +31 +/- 5 beats . min-1; CSD: -37 +/- 5 mmHg and -56 +/- 10 beats . min-1), quiet wakefulness (CO: +37 +/- 5 mmHg and +38 +/- 4 beats . min-1; CSD: -34 +/- 4 mmHg and -53 +/- 8 beats . min-1) and synchronised sleep (CO: +36 +/- 5 mmHg and +37 +/- 4 beats . min-1; CSD: -36 +/- 4 mmHg and -52 +/- 6 beats . min-1). Desynchronised sleep was associated with an identical response to CSD (-30 +/- 4 mmHg and -51 +/- 7 beats . min-1) but with a reduced (p less than 0.01) reflex response to CO (+18 +/- 3 mmHg These data indicate that carotid sinus baroreflexes largely maintain their ability to modulate pressure upwards and downwards when blood pressure has been reset at somewhat higher levels by standing and fighting and at somewhat lower levels by synchronised sleep. The selective depression of carotid occlusion responses during desynchronised sleep suggests a central or peripheral shift of the baroreflex stimulus-response curve or a selective central inhibition of the reflex response to baroreceptor unloading.