Based on available surface area for cell attachment, a 1 l microcarrier culture is equivalent to approximately 25 × 850 cm 2 roller bottles in terms of potential virus production capability (Table 1) . A typical growth curve for CR2 cells on Cytodex 1 microcarriers is shown in Figure 6 . Cells multiplied exponentially during the first 4 days before reaching stationary phase. A cell density of 1.5-2.0 × 10 9 total cells was typically obtained after approximately 100 h growth. At this density a confluent monolayer of CR2 cells covered the microcarriers (Figure 3 ). At 100% confluency the cells appeared elongated, resembling the surface of a golf ball. Cells ready for harvest exhibited complete CPE (Figure 4 ) 60-72 h after infection. The cultures were harvested before they became detached from the microcarriers. The morphological appearance of the cells at both critical stages was identical to the appearance observed in roller bottle cultures. Infectious DISC-HSV released from the CR2 cells was quantified using a TCID 50 assay and compared to the amount obtained from the roller bottle culture harvests. The results are shown in Table 1 . Typically 1.5-2.0 × 10 10 total pfu from a 1 l culture was regularly achieved, with approximately a 20 hour period during which the culture could be harvested without significant decrease of the titre. The total surface area available in the culture is equivalent to 25 roller bottles. This enables a comparison in terms of productivity to be made. We routinely achieve 2.0-2.5 × 10 10 total pfu from 25 roller bottle cultures. Therefore, the two production systems yield similar total amounts of DISC-HSV.