This paper describes a method for detecting oxygen consumption of adherent cell cultures. The sensing is based on oxygen-dependent quenching of the phosphorescence of a Pt-porphyrin complex immobilized on microcarrier beads, which are used as the cell culture substrate. Bead injection, a recent variant of the flow injection technique, is used to pack an aliquot of the beads into a small sensing layer that can be easily and rapidly renewed. The technique is tested on a model system of Chinese Hamster Ovary M1 cells grown on Cytodex-3 microcarrier beads. Cellular respiration is monitored through O2 consumption measured across a period of 3 min. The method is validated by detecting the impairment of aerobic metabolism caused by 1.5 mM amobarbital. Further, it is shown to have enough precision to distinguish even more subtle changes, such as the increase in oxygen consumption caused by stimulation of the muscarinic m1 receptor with 100 microM carbachol.