Abstract: A polynucleotide, comprising a contiguous nucleotide sequence coding for a human antibody with factor VIII specificity, or complementary to a nucleotide sequence coding for a human antibody for factor VIII specificity, or capable of selectively hybridizing under stringent conditions to such nucleotide sequence. Such polynucleotide may be used as a probe or primer for detection of factor VIII inhibitors, or be used for producing a recombinant polypeptide. A polypeptide, comprising a contiguous amino acid sequence corresponding to or mimicking a fragment or derivative of a human antibody with factor VIII specificity capable of specific binding to factor VIII. An antibody, comprising a recombinant human antibody with factor VIII specificity or an anti-idiotypic antibody directed against a human antibody with factor VIII specificity. Pharmaceutical compositions which contain such polypeptide or antibody.