Sensitive, monoclonal antibody-based, enzyme-linked immunosorbent assays (ELISAs) for plasma factor VIII (FVIII) antigen have been developed. The assays used five monoclonal anti-FVIII antibodies with known epitopes in four different pairwise combinations. The sensitivity of the assays was increased by use of the ELISA amplification method described by Bobrow et. al. (J. Immunol Methods 125:279, 1989). These assays can distinguish between CRM positive, CRM reduced and CRM negative hemophilia A. A total of 94 plasma samples from 78 different patients were screened and generally consistent results were obtained among the different assays. Such assays are potentially useful in the phenotypic and genotypic analysis of hemophilia A.