Recombinant factor VIII concentrates are stable when administered in a reconstituted form according to the manufacturer’s specifications, and undiluted via infusion with syringe mini‐pumps. However many Haemophilia centres administer recombinant factor VIII further diluted in intravenous fluids for greater ease of administration. To investigate the stability of recombinant factor VIII during administration as a diluted infusion, reconstituted factor VIII was stored in polyvinylchloride (PVC) mini‐bags undiluted (146 IU mL–1) and at factor VIII concentrations of 10 IU mL–1 and 2 IU mL–1. After 48 h of storage at room temperature in PVC mini‐bags, the recoveries of factor VIII activity were 41.9% of the initial activity for the undiluted (146 IU mL–1) product and 43.7% of the initial activity for factor VIII diluted to 10 IU mL–1. For factor VIII diluted to 2 IU mL–1, the amount of factor VIII activity remaining at 48 h was only 1.8% of the initial activity. In contrast, 100% of factor VIII activity was recovered after 48 h when undiluted reconstituted product (146 IU mL–1) was stored in a syringe. To investigate the mechanism of factor VIII activity loss during storage, factor VIII samples collected after 0, 3 and 48 h of storage were analysed by immunoblotting with factor VIII antibodies. No evidence of factor VIII proteolytic degradation during storage was found, however, large amounts of factor VIII antigen were recovered from the empty PVC mini‐bags following elution with denaturing detergent. We conclude that clinically significant losses of factor VIII activity occur during storage in PVC mini‐bags and that the loss of activity is most likely due to protein adsorption onto the plastic surface. This loss of factor VIII activity during storage in PVC containers may substantially affect the safety and potential cost savings of administering recombinant factor VIII by continuous infusion.