The solubility of carbon dioxide (CO2) in microbiological media at different pH values, water activities (a,), temperatures, buffering capacities and ratios of headspace to media volumes was determined by using a coulometer. Buffering capacity and ratio of headspace to media volume were shown to be the major factors influencing the solubility of CO, in modified atmosphere model systems. The growth inhibitory effects of different dissolved CO2 concentrations (0-50 ?mol ml-1) were determined for Pseudomanas fragi at 8°C and 22°C. Pseudomonas fragi was shown to be strongly affected by the CO2 concentration in the media. A carbon dioxide concentration of 40 ?mol ml-1 was needed to inhibit Ps. fragi at 8°C. The importance of measuring dissolved CO2 Concentrations in modified atmosphere packaging applications was shown and the coulometer proved to be an excellent tool for this purpose.