The cell inoculum for cultivation on microcarriers was prepared from late exponential CR2 cultures in 850 cm 2 roller bottles. Cultures were inoculated at a density of approximately ten CR2 cells per microcarrier and 5 g of Cytodex 1 l −1 (Figure 2 ). Cell growth was monitored by estimating nuclei released from a sample of microcarrier culture taken from the reactor after incubation in 0.1 M citric acid containing 0.1% (w/v) crystal violet (Sanford et al., 1951) . Glucose and lactate concentrations were determined using an off-line YSI 2700 glucose/lactate analyser (YSI, U.K. Ltd). Glucose and lactate concentrations were controlled by partial media changes on days 2 and 3 for the 1 l culture and days 2, 3, 4 and 5 for the 15 l culture. The 15 l culture was maintained for an additional 48 h period compared to the small scale 1 l cultures in Figure 5 . The bionebuliser is a low pressure shear disruption method which uses nitrogen as a carrier gas. The disrupter is depicted here schematically indicating how the process disrupts cells. Using a carrier gas pressure of 50 psi cells are drawn up and nebulised. This cell mixture is directed to a ceramic ball bearing where they impact. The cells are disrupted to release the virus and the whole disrupted cell/virus solution is collected. order to provide a maximal cell density at the point of infection.