The ability of optical oxygen sensors to monitor the levels of oxygen in raw and cooked beef was investigated. Raw and cooked beef slices were vacuum packaged and cooked beef slices were modified atmosphere packaged MAP, (60% N(2): 40% CO(2)) and held under refrigerated display (4 °C) for 15 or 35 days for MAP and vacuum packed samples, respectively. Oxygen sensors attached to the inside of the lidding material in modified atmosphere packages, or inserted into vacuum packages, were capable of monitoring changes in oxygen levels in all packaged samples. Lipid oxidation of samples was measured at regular intervals. Oxygen contents detected, ranged from 1.15 to 1.26% and 0.07-0.55% in MAP and vacuum packed samples, respectively. Samples containing greatest levels of oxygen were most oxidised and cooked samples were significantly (P<0.05) more oxidised than raw samples.