Monoclonal antibodies (MAbs) against ricin toxin (RT) and its subunits were produced in mice. The MAbs were initially selected based upon the ability to either bind ricin or the individual subunits in a solid-phase enzyme-linked immunosorbent assay (ELISA). Several candidates were selected for further evaluation, including their ability to inhibit ricin intoxication in vitro and their utility as immunodiagnostic reagents. Although their ability to capture antigen when bound to the solid phase was poor, some MAbs demonstrated potential utility as detection reagents in solid-phase immunoassays. Several MAbs were also able to inhibit ricin-mediated eukaryotic cell cytotoxicity in vitro. These MAbs may prove useful for preventing and/or treating ricin intoxication.