Cytodex 1 microcarriers can be used as a Vero cell culture support for the production of DISC-HSV virus. It could be envisaged that the microcarrier washing and conditioning procedure at a large manufacturing scale could be extremely time consuming. It is expected that the microcarriers will be sterilised in-situ inside the production vessels. Preliminary work at 35 l scale employs the use of an internal sieve to aid the washing and conditioning process. At present at the 35 l scale this step takes approximately 2 h to complete. This washing and conditioning step may be an extensive time constraint at a manufacturing scale. Tackling the engineering problem in terms of pipe work and increasing flow rates could reduce this time. This is an issue that is under review and will require suitable development time to reduce it satisfactorily. Yields achieved from the microcarrier cultures were comparable to those obtained in the standard roller bottle culture systems (Table 1) .