A popular garlic preparation containing 1.3% allicin at a large dose (2400 mg) was evaluated in this open-label study in nine patients with rather severe hypertension (diastolic blood pressure > or = 115 mm Hg). Sitting blood pressure fell 7/16 (+/- 3/2 SD) mm Hg at peak effect approximately 5 hours after the dose, with a significant decrease in diastolic blood pressure (p < 0.05) from 5-14 hours after the dose. No significant side effects were reported. Our results indicate that this garlic preparation can reduce blood pressure. Further controlled studies are needed, particularly with more conventional doses (e.g., < or = 900 mg/day), in patients with mild to moderate hypertension and under placebo-controlled, double-blind conditions.