Background: IgG to galactose-alpha-1,3-galactose (alpha-gal) are highly abundant natural antibodies (Ab) in humans. alpha-Gal-specific IgE Ab cause a special form of meat allergy characterized by severe systemic reactions 3-7 h after consumption of red meat. We investigated 20 patients who experienced such reactions and characterized their alpha-gal-specific IgE and IgG responses in more detail. Methods: alpha-Gal-specific IgE was determined by ImmunoCAP. IgE reactivity to meat extract and bovine gamma globulin (BGG) was assessed by immunoblotting and ELISA, respectively. In some experiments, sera were pre-incubated with alpha-gal or protein G to deplete IgG Ab. alpha-Gal-specific IgG(1-4) Ab in individuals with and without meat allergy were assessed by ELISA. Results: In immunoblots, BGG was the most frequently recognized meat protein. Binding of IgE and IgG to BGG was confirmed by ELISA and completely abolished after pre-incubation with alpha-gal. Neither the depletion of autologous alpha-gal-specific IgG Ab nor the addition of alpha-gal-specific IgG Ab from nonallergic individuals changed the IgE recognition of BGG of meat-allergic patients. Meat-allergic patients showed significantly higher alpha-gal-specific IgG1 and IgG3 Ab than nonallergic individuals, whereas the latter showed significantly higher levels of alpha-gal-specific IgG4 Ab. Conclusion: Patients with delayed meat allergy display IgE and IgG Ab that selectively recognize the alpha-gal epitope on BGG. Their enhanced alpha-gal-specific IgE levels are accompanied by high levels of alpha-gal-specific IgG1 devoid of IgE-blocking activity. This subclass distribution is atypical for food allergies and distinct from natural alpha-gal IgG responses in nonallergic individuals.