Described is a process for producing poliovirus, the process comprising: a) providing a serum-free suspension culture of cells, which are primary human retina (HER) cells that have been immortalized by expression of adenovirus E1 sequences, b) infecting the cells with poliovirus, at a cell density of between 2×106 cells/ml and 150×106 cells/ml, and c) harvesting poliovirus at a time of between 12 and 48 hours after infection.