Factor VIII inhibitors are produced during or after coagulation factor VIII (FVIII) therapy in hemophilia A patients. These inhibitors are usually detected by a modified Bethesda assay or an enzymelinked immunosorbent assay (ELISA). In this study, we used the Bethesda assay to determine the incidence of FVIII inhibitors in 75 fresh plasma samples obtained from 50 hemophilia A patients, and then used ELISA and the Bethesda assay to determine the titres of these inhibitors after the samples had been frozen and thawed. The samples from the screening Bethesda assay were centrifuged and stored at -70degrees C in accordance with the assay guidelines. Subsequently, these samples were thawed and analyzed using ELISA and the Bethesda assay. The incidence of inhibitors in hemophilia A patients was 20.0%. Among the 35 inhibitor-positive samples identified in the screening Bethesda assay, 16 were positive in ELISA while only 4 were positive in the repeated Bethesda assay. In this study, the ELISA technique showed a higher sensitivity than the Bethesda assay in the detection of FVIII inhibitors in samples that were subjected to freezing and thawing procedures; this was because the Bethesda assay could not identify the FVIII inhibitors that were degraded after freezing and thawing.