Healthy ambulatory subjects took 6 different MAO inhibitors (MAOIs) orally for 2 to 4 weeks. The new reversible MAO-A inhibitors brofaromine and moclobemide were compared with the irreversible MAOIs clorgyline, selegiline, phenelzine and tranylcypromine. Pressor responsiveness to oral tyramine was assessed before, during and after treatment. In unmedicated subjects, doses of tyramine to raise systolic blood pressure by at least 30 mmHg (PD30) ranged between 200 and 800 mg. During treatment with MAOIs, the PD30 decreased. The ratio of median effective doses (ED50) of tyramine (pre- vs post-treatment) was: selegiline 5, moclobemide 7, brofaromine 10, clorgyline 10, phenelzine 13 and tranylcypromine 55. Pressor responsiveness normalized within 8 days after stopping the reversible MAOIs and 30 days after tranylcypromine. The increased sensitivity after phenelzine persisted for longer than 8 weeks and after clorgyline for longer than 15 weeks. The results suggest that the two reversible MAO-A inhibitors moclobemide and brofaromine carry a much reduced liability to tyramine-related hypertensive reactions.