Different types of microcarriers were assessed for the large-scale culture of influenza virus in the Madin-Darby canine kidney (MDCK) cells. Both porous and solid carriers were examined. A higher titre of influenza A/PR8/34 virus was recovered from cultures using solid (1.3x10(9) PFU per ml) rather than porous carriers (4.0x10(8) PFU per ml). High titres of virus (1.0x10(9) PFU per ml) were also obtained from roller bottle cultures of MDCK cells and the traditional culture technique using embryonated hens' eggs (3.9x10(9) PFU per ml). We found that solid carriers composed of dextran with a positive charge are the most suitable carriers for the large-scale growth of influenza A virus in MDCK cells using serum-free media.