This investigation will utilize a systematic determination of anti-FVIII antibody specificity in PTPs (> 50 ED) with hemophilia A who have developed inhibitors in response to treatment with any FVIII product(s). A group of patients with hemophilia A, who have no evidence of current or prior FVIII inhibitor will be included for comparison. The objective of this study is to describe the patterns of antibodies and associated epitopes in the study population.

Inclusion Criteria:

· Patients with moderate or severe congenital hemophilia A, a current FVIII inhibitor, who have taken at least two different FVIII products during their lifetime.

Exclusion Criteria:

• Patients who have had an inhibitor prior to their current inhibitor.
• Patients with immune disorders.