Ultrafiltration is frequently used in the biotechnology industry for protein purification. The main applications of ultrafiltration are for protein concentration and buffer exchange. This paper focuses on ultrafiltration for purification of parvovirus. The feasibility of using ultrafiltration to remove contaminating host cell proteins from the virus particles has been investigated. Purification of virus particles and virus vectors for clinical applications of gene therapy and in the manufacture of viral vaccines is a major large-scale separations problem. Today, parvoviruses, such as adeno associated virus, are being extensively investigated as gene therapy vectors. Consequently, development of robust purification operations will be essential. Tangential flow ultrafiltration and high performance tangential flow filtration of Aedes Aegypti densonucleosis virus has been investigated using flat sheet membranes with a nominal molecular weight cut off of 100 and 300 kD. Virus particles were detected in the permeate of the 300 kD membrane for both modes of operation. In tangential flow filtration no virus particles were detected in the permeate from the 100 kD membrane. However, during high performance tangential flow filtration significant passage of virus particles through the membrane was observed. The results obtained here are in general agreement with results obtained in previous studies of high performance tangential flow filtration for protein purification. Optimization in the operating conditions of high performance tangential flow filtration may result in a highly selective unit operation for purification of virus particles and virus vectors.