Patients with hymenoptera venom anaphylaxis before immunotherapy (n = 50) showed significantly lower renin, angiotensinogen, angiotensin I and angiotensin II as compared to healthy non-allergic controls (n = 25) (p < 0.05). A significant inverse correlation between the severity of clinical symptoms and the plasma levels of renin, angiotensinogen, angiotensin I and angiotensin II was found: the lower the levels the more severe the clinical symptoms. Hymenoptera venom allergic patients with repeated anaphylactic reactions during hyposensitizatin did not tolerate the sting of a living insect (n = 6). Sting provocation with a living insect induced clinical symptoms of anaphylaxis in all of the 6 patients. Renin, angiotensinogen, angiotensin I and II remained significantly lower in these patients as compared to healthy non-allergic controls. Likewise, no stimulation of the renin angiotensin system occurred during the anaphylactic reaction. The values of angiotensin II were similar or lower than the values before the anaphylactic reaction. In contrast, patients with successful immunotherapy (n = 27) who tolerated the sting of a living insect, renin, angiotensin I and II were significantly higher than in patients without immunotherapy. After immunotherapy, the values for renin, ANG I and ANG II were similar to the values found in healthy non-allergic controls. Patients with a history of hymenoptera venom anaphylaxis (n = 22) showed significantly lower ANG II concentrations in their leukocytes as compared to healthy non-allergic controls (n = 24). Successful immunotherapy induced a significant 9-fold increase in ANG II as compared to patients without immunotherapy. These findings suggest a possible role of the renin angiotensin system in hymenoptera venom anaphylaxis.