Pargyline is an irreversible inhibitor of monoamine oxidase (MAO) that is used clinically to treat moderate hypertension. At 10 mg/kg iv, pargyline induces a moderate decrease of systolic blood pressure in unanaesthetized hypertensive rats but not normotensive WKR or Sprague-Daley rats. The correlation between the fall of blood pressure and the inhibition of brain MAO suggests that the accumulation of amine in brain is responsible for the fall in pressure. Reactive oxygen species-mediated monocyte hypertrophy is prevented by pargyline at a concentration of 10 µM.