Severe allergic reactions during specific immunotherapy may occur in the treatment of hymenoptera sting allergy. The objective of the present study was to examine the characteristics of allergic reactions during specific immunotherapy in patients with allergy towards hymenoptera venom in the Iranian population. A prospective study was performed using the clinical reports of 27 patients with anaphylaxis to bee venom (Apis melifera, Geupes vespula and Geupes Polites). Ten patients treated with Cluster protocol during 2002 and 2006 After diagnosis of hymenoptera sting allergy according to history and intradermal tests, the patient were treated with Cluster protocol immunotherapy. The protocol lasted 6 weeks with an increase in the concentration of venom from 0.01 microg/ml to 100 microg/ml. None of the patient received premedication. All patients with hymenoptera venom allergy received 120 injections. Anaphylactic reactions were classified according to the Mueller-classification. The frequencies of systemic reactions during Cluster protocol were 8.33% and 5% for yellow jacket and honey bee venom respectively. No patient experienced severe systemic reaction. Cluster protocol for hymenoptera immunotherapy is a reliable method for the treatment of anaphylactic reactions to bee venom. It is safe with low cost and do not need hospitalization.