The astigmatid mite Sarcoptes scabiei is the causative agent of scabies, a highly infectious parasitic disease of the skin. Although the mite causes marked hypersensitivity reactions, particularly in crusted (severe) scabies, little is known about the specific scabies mite molecules involved in such immunologic responses. We have identified six genes encoding scabies mite homologues of mu and delta-like glutathione S-transferases (GSTs) as well as novel house dust mite GSTs. A mu class S. scabiei GST was subcloned into a prokaryotic expression system. The purified recombinant protein rSsGST01 reacted strongly with IgE and IgG4 in sera from crusted scabies patients. This response was not observed with control antigens or with ordinary scabies and uninfested patient sera. In addition, the specific IgE response to rSsGST01 did not correlate with the total IgE level of the patient. These results suggest that GST may play a role in the pathophysiology associated with crusted scabies.