The present invention describes the preparation and use of biologically and immunologically active humanized monoclonal antibodies to Shiga toxin, a toxin associated with HC and the potentially life-threatening sequela HUS transmitted by strains of pathogenic bacteria. The present invention describes how these humanized antibodies may be used in the treatment or prevention of Shiga toxin induced diseases. One aspect of the invention is the humanized monoclonal antibody which binds Shiga toxin where the constant regions are IgG1-kappa and the variable regions are murine in origin. Yet another aspect of the invention is expression vectors and host cells transformed with such vectors which express the humanized monoclonal antibodies of the present invention.