A method for the growth of cells in a nutrient medium, which comprises causing the nutrient medium to flow upwardly with decreasing velocity, substantially without turbulent flow, and allowing cells to grow at an equilibrium level in the flow. The method can be conducted in apparatus comprising a vessel (1) of increasing and then decreasing cross-section (greatest at 2) in the direction of flow from a bottom inlet (3) to a top outlet (4). The used medium can be regenerated, if desired.
