Microcarriers are small solid or in some cases immiscible liquid spheres, on which cells may be grown in suspension culture. They provide a means of obtaining large yields of cells in small volumes. The cells must exhibit anchorage dependence of growth and the dimensions of the carrier bead may be important in controlling growth rate. Microcarriers are support matrices allowing for the growth of adherent cells in bioreactors. Carrier materials for cells may be composed by gelatin, porous glass, collagen or cellulose, with dimensions of 170 - 6000 µm. Well known brands include Cytodex™, (Pharmacia) or Cultispher™ (Hyclone).