The immunocytochemical localization of the metallothioneins (MT), a family of low molecular weight, heavy metal binding proteins, was investigated in rat and human spinal cord using two distinct antibodies. Polyclonal antibodies were raised to the peptide (SCKCKECKCTS), an epitope common to all human MT isoforms. The monoclonal antibody, E9 which recognizes a different epitope of the MT protein, was also used. Similar results were obtained with either antibody. Both antibodies recognized authentic MT from rabbit liver and horse kidney on Western blots. Immunoreactivity was localized primarily in the cytoplasm of motoneurons in the anterior horn of cervical and lumbar cord. However nuclear staining was present in some motoneurons in both rat and human cord. Intense nuclear, as well as cytoplasmic staining was seen in astrocytes. Capillary endothelia, ependymal cells, arachnoid and pia were also positive for MT.