A controlled study using matched placebo in 22 ambulatory patients demonstrated furazolidone to be hypotensive in divided doses of 300 to 1250 mg daily. Calculated mean arterial pressure was reduced 28 mm Hg and pulse pressure was diminished. Onset of action usually occurred in 1 week with maximum effect in 3 to 4 weeks. The exact mechanism of blood pressure reduction remains obscure. Tachyphylaxis, and adverse effects, especially weight loss, gastrointestinal symptoms and stool flora changes limit application of the drug in the treatment of patients with hypertension. Hopefully, derivatives may be developed which disassociate the hypotensive from the unwanted effects.