By screening an expression library of Echinococcus granulosus with IgE from sera of patients with cystic echinococcosis (CE) and allergic reactions, we isolated the C-terminal region of a new heat shock protein (HSP)70 of E. granulosus. The protein, named Eg2HSP70, has close homology with the C-terminal region of Dermatophagoides farinae and human HSP70. We investigated the humoral and cell-mediated immune responses to this antigen in patients with CE grouped according to the presence of allergic reactions. Immunoblotting detected total IgG, IgG4 and IgE specific to Eg2HSP70 (83% of sera contained IgG, 31% IgG4 and 57% IgE). No significant difference was found in immunoglobulin percentages according to the presence of allergic reactions. Immunoblotting inhibition showed that no IgG or IgE specific to Eg2HSP70 cross-reacted with D. farinae or human HSP70. Eg2HSP70-stimulated PBMC from 26 patients produced significantly greater amounts of TNF-alpha, IFN-gamma, and IL-10 than unstimulated cultures in all patients, irrespective of the presence of allergic reactions (P < 0.05). They also produced significantly greater amounts of IL-4 than unstimulated cultures exclusively in patients with allergic reactions (P < 0.05). These findings show that Eg2HSP70 is a new antigenic molecule inducing both B and T cell responses.