Apparatus for growing tissue cultures in vitro, which permits a concentration gradient of nutrients to develop through a permeable membrane to which a sample of tissue is attached. The permeable membrane is attached to the bottom end of a tubular support that in turn hangs by a flange connected to its upper end on the top of a well containing the nutrients. Typically, the well is part of a tissue culture cluster dish. The flange of the support positions the support and membrane centrally in the well so as to avoid capillary action in the space between the well and support. The configuration of the support and its cooperation with the lid of the cluster dish also prevents the support and membrane from floating in the nutrient solution in the well. Openings in the support provide access for a pipette to add and withdraw fluid from the space between the well and membrane support and from the space below the membrane.