In pentobarbitalized closed-chest dogs, nicergoline (10--100 microgram/kg, i.v.) reduced blood pressure, heart rate, and splanchnic nerve activity. Intracisternal administration of nicergoline (3 microgram/kg) only reduced splanchnic nerve activity. In open-chest dogs, nicergoline reduced blood pressure, cardiac output, and total peripheral resistance but did not change heart rate. In pithed rats treated with a beta-adrenoceptor-blocking agent, nicergoline reduced the pressor responses to noradrenaline and adrenaline. Nicergoline slightly attenuated the pressor responses of dogs to noradrenaline and tyramine and, in addition, reversed the hypertension induced by adrenaline and dimethylphenylpiperazinium. Nicergoline (100 microgram/kg) increased the tachycardia induced in dogs by stimulation of the right cardiovascular nerve and prevented the inhibitory effect of clonidine on this response. However, nicergoline only partially antagonized the effect of clonidine once it was fully established. Nicergoline did not antagonize the hypotensive and bradycardic effects of clonidine when they were established. Nicergoline did not affect the vagally mediated bradycardia evoked by carotid nerve stimulation in beta-adrenoceptor-blocked dogs. The compound did not change blood pressure in Cl spinal cord transected dogs. In conclusion, nicergoline appears to decrease blood pressure by blocking alpha-adrenoceptors and, at least at some doses, by a central inhibition of the sympathetic tone. Nicergoline appears to be a preferential alpha 1-adrenoceptor-blocking agent.