Ethylene production in relation to O2 partial pressure of whole pear fruit stored at 2 °C could be described by a Michaelis-Menten equation. This was indicated by the use of a gas exchange model. The maximum ethylene production rate was strongly inhibited while the K(mO2) value (1.25 kPa) was not affected by elevated CO2. Ethylene production was also inhibited by 1-MCP, an inhibitor of ethylene perception. The reduction in ethylene production by CO2 was similar for 1-MCP treated and untreated pears. Elevated CO2, therefore, must have had an influence on ethylene production other than through ethylene perception. A possible site of inhibition by CO2 is the conversion of ACC to ethylene. The O2 uptake rate in relation to O2 partial pressure of whole pear fruit could be described by a Michaelis-Menten equation. The O2 uptake rate was inhibited by elevated CO2 at a level similar to the inhibition of ethylene production. Again the K(mO2) value (0.68 kPa) was not affected by CO2. Using 1-MCP treatments it was shown that there was no direct effect of inhibited ethylene production on O2 uptake rate.