BACKGROUND Immediate-type allergies to bumblebee stings occur infrequently. Previous studies have demonstrated a high degree of cross-reactivity between honeybee venom (HBV) and bumblebee venom (BBV). It has been proposed that venom immunotherapy (VIT) with HBV is a therapeutic alternative for patients with BBV allergy. RESULTS We present two cases of occupational immediate-type allergies to BBV. Although both nonatopic patients had a negative personal history of previous allergic reactions to honeybee sting, specific IgE antibodies and a positive intradermal reaction to HBV were detected. Despite VIT with HBV, the two developed another severe allergic reaction after incidental bumblebee stings. VIT with BBV, using in one patient a rush protocol and in the other a "conventional" regimen, with escalating doses of 0.01-100 microg of BBV, was performed. Before and during the VIT, the course of IgE and IgG specific antibodies to BBV was analyzed, demonstrating a significant decrease of BBV-IgE and an increase of BBV-IgG. The effectiveness of the treatment was also proven by an in-hospital sting challenge with a live bumblebee. CONCLUSIONS Our data demonstrate that cross-immunotherapies with HBV do not protect BBV-allergic patients sufficiently. We conclude that BBV-allergic patients should be treated with BBV. A "rush" VIT with BBV is a safe alternative to a "conventional" protocol.