Methods for producing biological solutions such as immunoglobulins and in
particular anti-D immunoglobulin substantially free of abnormal prion
protein resulting therefrom. Specifically provided are methods for
aggregation of prions and depth filtration of the biological solution to
capture and remove abnormal and if desired, normal prion protein. The
prion protein may then be eluted from the depth filter and filter washes
and concentrated sufficient for detection at limits currently required by
available assays.