The ACE genes have 2 allelic forms, “I” and “D.” The “D” genotype has both highest angiotensin-II generation and serum ACE levels compared to “I”.120 patients with IgE-anaphylaxis, 119 healthy controls, and 49 atopics had serum ACE levels, ACE genotype, and renin levels determined.Plasma renin levels were identical for all groups.Serum ACE levels and genotypes were similar for healthy controls (HC) and atopics, but lower in anaphylaxis (P = 0.012), with ACE genotypes also showing increased “I” genes (P = 0.009). Here, REN is linked to anaphylaxis.