The introduction of new factor concentrates has, at times, resulted in an increase in inhibitor development; hence large systematic surveys of inhibitor development are necessary whenever new products are introduced. This study presents the results of a surveillance study conducted by the Inhibitor Subcommittee of the Association of Hemophilia Clinic Directors of Canada that evaluated inhibitor development in patients with haemophilia A following the switch to a second generation recombinant FVIII product (rFVIII-FS; Kogenate((R)) Bayer). Four hundred and sixty haemophilia A paediatric and adults patients from 17 Canadian Comprehensive Hemophilia Care Centers were enrolled in the study. Of these, 274 patients had evaluable data. Blood samples collected at baseline (prior to the switch to rFVIII-FS), and at 12 and 24 months following conversion were tested for inhibitors by the Nijmegen-modified Bethesda assay. Four subjects had positive inhibitor titres at baseline, with values ranging from 3.3 to 160 BU. Of the 274 patients who had baseline samples collected, 225 had postswitch samples collected at 12 months and 189 subjects had samples collected at 24 months. Only patients with positive baseline inhibitor titres (n = 4) had positive inhibitor titres at either the 12- or 24-month postswitch time points; therefore no de novo inhibitors developed over the 2-year evaluation period in this patient population. The results of this surveillance study suggest that the altered formulation of this recombinant FVIII concentrate was not associated with an increased incidence of inhibitor formation.