The present invention relates to a bi-specific antibody or antibody fragment having at least one arm that is reactive against a targeted tissue and at least one other arm that is reactive against a linker moiety. The linker moiety encompasses a hapten to which antibodies have been prepared. In preferred embodiments, the hapten is histamine-succinyl-glycine (HSG). In more preferred embodiments, the at least one arm comprises the CDR sequences of the HSG-binding 679 antibody. The antigenic linker is conjugated to one or more therapeutic or diagnostic agents or enzymes. In one embodiment, the invention provides constructs and methods for producing the bispecific antibodies or antibody fragments, as well as methods for using them.