The metabolic activity (glucose consumption and lactate production) of L-929 cells in a liquid/ liquid interface system (culture medium/fluorocarbon) has been investigated in long-term culture. The specific glucose consumption rate and specific lactate production rate at the interface were found to be higher than those at a polystyrene surface. This result can be related to the fact that the cell adhesion at the interface is weaker than that at a polystyrene surface. It was suggested that cell culture at the interface could be significant in raising yields from animal cell bioreactors.