An enzyme-linked immunosorbent assay (ELISA) was developed to detect Crimean-Congo hemorrhagic fever (CCHF) virus-specific immunoglobulin M (IgM) in human serum samples. For this test, a heat-inactivated antigen was prepared from the brains of suckling mice infected with CCHF virus. The IgM-capture ELISA proved more sensitive than indirect fluorescence tests for IgM to this virus. A human serum containing high-titer IgM to CCHF virus was used for an antigen-capture ELISA to detect this virus in heat-inactivated suspensions of virus-infected ticks. The antigen-capture ELISA appeared to be as sensitive as virus isolation in suckling mice. The studies described suggest that the IgM-capture ELISA and the antigen-detection ELISA should provide a rapid and sensitive diagnosis of human CCHF virus infection and should be useful in ecologic studies of this virus.