Genotypes and haplotypes were assessed, including SNPs rs2781659(A>G), rs2781667(C>T), rs2246012 (T>A) e rs17599586 (C>T) ofARG1 and rs3742879 (A>G) e rs10483801 (C>A) ofARG2. While no associations were found of the SNPs andhaplotypes with Sildenafil responsiveness, we found that variant genotypes CT ofrs2781667(C>T), AG of rs2781659(A>G) and CT+TT of rs17599586(C>T), aswell as GTTT haplotype of ARG1, were associated with a reducedarginase activity on plasma in clinical erectile dysfunction group. This evidence concerns the gene ARG1 and erectile dysfunction.