It is not well understood how changes from suspension to microcarrier cultures affect cell growth, metabolism, and yield of recombinant proteins. To investigate the effects of culture conditions on cell characteristics, fed-batch bioreactor cultures were performed under different culture conditions ( suspension cultures, cultures attached to Cytodex 3 and Cytopore 1 microcarriers) using two different Chinese hamster ovary cell lines producing either secreted human placental alkaline phosphatase ( TR2-255) or tissue plasminogen activator ( CHO 1-15-500). In controlled, agitated bioreactors, suspension cultures reached cell densities and product titers higher than those in microcarrier cultures, in contrast to the results in static flask cultures. Growth and metabolic activities showed similar trends in suspension and microcarrier culture regardless of cell line. However, the responses of the specific productivities to the different culture conditions differed significantly between the cell lines.