Abstract: The invention is a flow-through bioreactor for the retention and culture of cells in perfused media. The bioreactor is a generally rectangular vessel with inlet and outlet ports in the lid allowing for media flow along the longitudinal axis of the vessel. The inner surface of the bottom wall of the bioreactor has a plurality of generally rectangular grooves having a length, a depth, and a width. The grooves are positioned in the bottom wall such that their length is transverse to the longitudinal axis of the vessel, allowing media flow across the width of the grooves. Cells settle into the grooves, where they proliferate and differentiate, without entering the bulk flow of media through the vessel, thus avoiding loss of cells due to media flow. The preferred grooves have a width to depth ratio of about 1:1 or 2:1. The preferred width of the grooves is about 50 .mu.m to about 5,000 .mu.m, and the preferred depth is about 50 .mu.m to about 5,000 .mu.m.