A process of flocculating microbial cell material from a suspending medium which contains cell material, comprising adding to the suspending medium a first polymeric material which is cationic and has intrinsic viscosity of not more than 2 dl/g, and subsequently or simultaneously adding to the suspending medium a second polymeric material which is cationic or substantially non-ionic and has intrinsic viscosity of at least 4 dl/g, and allowing the cell material to flocculate.