The cell and virus harvests from either pooled roller bottle cultures or microcarrier cultures were passed through a bionebuliser (Glas-Col) at a pressure of 50 psi using sterile filtered nitrogen as the carrier gas. The carrier gas causes a vacuum over the hole leading to the cell suspension. This vacuum draws the cell suspension up the tubing and allows the cell suspension to become mixed with the carrier gas. The mixture then flows through the orifice to impact on the target a ceramic ball to disrupt the cells in the suspension. The flow rate of the gas determines the density of cells in the mixture and the target ceramic ball can be adjusted to maintain a good bionebulisation of the cells. The process is depicted in Figure 5 . This low-pressure shear system has been used previously to disrupt cells (Degouys et al., 1997) .