The 70-kDa heat shock proteins (hsp70) are a highly conserved, abundant, and ubiquitous family of proteins expressed by all organisms from bacteria to humans. It is well established that hsp70 family members function as molecular chaperones and aid in the intracellular folding of newly synthesized or denatured proteins. Current evidence suggests an emerging role for hsp70 family members in immune responses and in clinically important responses to stress and tissue damage. Here we report the generation and characterization of several MAbs to hsp70 family members. Immune responses to this highly conserved family were induced in mice by immunization with synthetic peptides that contain regions of the mouse mitochondrial hsp70 coupled to a potent helper T cell epitope derived from tetanus toxoid. The resulting MAbs include ones specific for the human and mouse mitochondrial hsp70 and others that show cross-reactivity among the family members and recognize the mitochondrial hsp70, the endoplasmic reticulum resident hsp70, Bip/grp78, the constitutively expressed cytosolic hsp70, hsc70, and the heat-induced member, hsp70. Significantly, these MAbs are effective in Western blotting, in immunoprecipitation, and in immunofluorescence, and thus should find applications in the purification and detection of members of this important family.