Chronic (21 days) treatment with the selective monoamine oxidase (MAO)-A inhibitor clorgyline, but not with the MAO-B inhibitor deprenyl in pithed rats leads to increased blood pressure responses to sympathetic stimulation and intravenous tyramine, and to elevated unstimulated heart rates. No significant changes are observed in plasma catecholamine responses to sympathetic stimulation, nor in beta-adrenoreceptor numbers in heart ventricles. These findings suggest that the hypotensive effects of MAO inhibitors result from central nervous system rather than peripheral nervous system alterations.