Three monoclonal antibodies generated by immunization of mice with Plasmodium berghei-infected red blood cells were found to react with the 75-kDa heat-shock protein (HSP70) present in liver stages and erythrocytic forms of the parasites. These antibodies were shown to react with a recombinant protein encoding the carboxyl terminal half of PfHSP70 (aa 365-681). Differently from earlier results, we clearly demonstrated that HSP70 was also expressed in the sporozoite stage, using these monoclonal antibodies in an immunofluorescence and Western immunoblot assay. These monoclonal antibodies react not only with sporozoites of P. berghei, the parasites originally used for the immunization, but also with sporozoites of several other rodent and human plasmodial species. Passive transfer of these monoclonal antibodies into naive mice, simultaneously injected with sporozoites, failed to neutralize the infectivity of P. berghei sporozoites and to inhibit the development of liver stages of P. yoelii.