An evaluation of a new Enzyme Linked Immunosorbent Assay (ELISA) factor VII:Ag assay in factor VII congenital deficiencies was carried out. This assay was compared to factor VII:C assay and the Inhibitor Neutralization Assay (INA) for factor VII:Ag, both in normals and F VII-deficient patients. The correlations between ELISA F VII:Ag and VII:C, as well as the one between INA F VII:Ag and VII:C, were good (r = .86 and .81, respectively). The correlation between the two immunologic methods of assay in normals was fairly good (r = 0.73, P less than 0.001); whereas in mild F VII deficiencies (heterozygotes for F VII deficiencies), the two methods correlated very well (r = .96). In the severe deficiencies, ELISA F VII:Ag assay allowed the evaluation of F VII protein levels below 1 u/dl. The sensitivities of the INA and ELISA assays were evaluated by creating artificially prepared plasmas containing serial amounts of purified F VII: INA was unable to pick up F VII protein levels lower than 75 ng/ml, whereas the ELISA assay could detect up to 5 ng of F VII.