An anti-TSST-1-specific monoclonal antibody (MAb 8-5-7) was tested for its protective capacity in a rabbit infection model to toxic shock syndrome (TSS). The challenge strain of Staphylococcus aureus (RN4710), which contained a plasmid encoding TSS toxin-1, was introduced into previously implanted chambers. Purified monoclonal antibody (1.25 mg of immunoglobulin G) administered parenterally 1 day before and 1 day after initiation of infection provided complete protection against the TSS-like syndrome and the mortality which occurred in unprotected rabbits.