Abstract Storage in carbon dioxide-enriched air increased the odorand color shelf-life of prepacked fresh beef by 3 to 10 and 1 to 9 days, respectively, depending on the CO 2 concentration, the initial number of bacterial cells on the meat surface and the storage temperature. Steaks of lean beef were inoculated with a mixture of psychrotolerant strains of Pseudomonas and Achromobacter , packaged in cardboard trays, overwrapped with a gas-permeable polyvinyl-chloride film, and incubated at 0-10 °C in air containing from 0-20% CO 2 . Fifteen percent CO 2 was the preferred concentration since it was nearly as effective as 20% and almost twice as effective as 10%. The smaller the inoculum and the lower the storage temperature, the greater was the effectiveness of CO 2 . Off-color rather than off-odor limited shelf-life in all cases. A short initial exposure of the inoculated meat to 100% CO 2 at 22 or —80°C was without effect on subsequent storage life in air. Carbon dioxide did not affect significantly changes in pH or weight loss due to weep during storage.