Purpose. The present study investigated whether L-arginine supplementation reduces blood pressure (BP) in hypertensive subjects with different ACE genotypes. Methods. Eight male hypertensive patients received L-arginine (2 or 4 g/day) or a placebo for a period of 4 days prior an exercise test. Statistical analysis consisted of one-way analysis of variance. Results. L-arginine supplementation induced a statistically significant (p ⋋ 0.05) reduction in systolic BP measured during rest (reductions of 7.8% and 12.3% with 2 and 4 g/day, respectively), exercise (reductions of 11.8% and 10.4% with 2 and 4 g/day, respectively), and recovery (reductions of 11.7% and 10.7% with 2 and 4 g/day, respectively). The observed magnitude of BP reduction suggests an association with ACE polymorphism; a larger effect was seen with the II and DI genotypes compared with the DD genotype (II: 121 mmHg and DI: 133 mmHg vs. DD: 144 mmHg). Conclusions. The results showed that L-arginine supplementation at low doses was efficient in reducing BP and that vasodilator actions that occurred through the secretion of nitric oxide might be ACE genotype dependent.