Abstract: The present invention provides an improved method and apparatus for growing biomass particles, particularly microcarrier-bound cells, in an agitated suspension culture vessel in which fresh culture medium is added and spent culture medium is withdrawn continuously or semi-continuously. The improvement comprises withdrawing the spent culture medium through a particle settling chamber located within the vessel and at least partially immersed in the agitated culture medium therewithin. The particle settling chamber comprises a hollow container with a bottom opening through which biomass particles, such as microcarrier-bound cells, settle by gravity back into the agitated culture medium and a top opening through which particle-free spent culture medium is withdrawn form the vessel. The settling chamber is configured such that the fluid velocity of culture medium entering the settling chamber through the bottom opening is significantly less than the biomass particle settling velocity.