A solution of pooled cryo-precipitate for preparing factor VIII (F VIII) by the solvent/detergent method was contaminated experimentally with parvovirus B19-positive plasma to evaluate virus reduction achieved by the final steps of the F VIII production process. Virus reduction was at least 2 logs of the total amount of B19 virus added to the pooled cryo-precipitate. The major amount of B19 virus was detected in the solution used to regenerate the F VIII-selective anion exchange chromatography column. A few viral particles were detected in the final F VIII concentrate before filtration but these were aggregates and were removed by filtration, and in the solution used to regenerate the anion exchange resin. It is not known whether the residual viral DNA present in the final product represents infectious or inactivated particles.