Transmissible spongiform encephalopathies are a group of fatal, neurodegenerative diseases commonly known as prion diseases. Prion diseases can resist traditional inactivation strategies and may be iatrogenically transmitted by surgical instruments through the human population. These properties have led to the need for a suitable detection method of the prion infectious agent, and increased pressure regarding the development of anti-prion cleaning methodologies that would ensure the safety of surgical instruments. Although other techniques have been applied, the animal bioassay remains the 'gold standard' method for assessing infectivity. As the vast majority of surgical instruments are made of stainless steel, and in order to test this surface using the animal bioassay, the application of very thin surgical stainless steel wires has been widely adopted. These wires are easily inoculated and may be reimplanted into animals without the requirement for elution of the residual material. However, their comparability to the dimensions, shape and size of surgical instruments is questionable. This article shows how such contaminated wires (residual protein between 6.3 and 16.0 ng/mm(2)) can be cleaned more easily than flat metal surfaces (residual protein between 63.9 and 89.3 ng/mm(2)) under comparable conditions using recommended cleaning agents. These results indicate that the application of wires as a realistic means of assessing the removal or inactivation of the prion infectious agent from surgical instruments should be treated with caution.