The present work concerns a study on the content and release of CO2 from Gruyère cheese during ripening. The CO2 content of the body of the cheese was determined monthly in the center, midway and at the outer edge of loaves of cheese by means of a recently developped method. The average value increase from ca. 0.81 to ca. 1.35 mmol CO2/100 g cheese during the first month (storage at 14°C and subsequently at 18°), remained practically constant during the second month (storage at 18°C) and decrease slowly (storage again at 14°C) until the end of the study (6 months) due to the gradual diffusion of the CO2. The highest concentration, which was found in the center of the loaf, (ca. 1.35 mmol/100 g cheese) was approximately 2.5 times lower than that measured in Emmental cheese. The release of CO2 from whole cheeses and from cheese rinds (smear) was follwed continuously by using equipment developped for this purpose. From the third to the eighth week, the released CO2 decreased rapidly from more than 225 to ca. 102 mmol/24 hours (storage at 18°C). After the eighth week, it remained significatively constant (102 mmol/24 hours) until the end of the study. Teh released CO2 seems to be essentially produced by the cheese smear. It was approximatively 2 to 3 times higher than that measured with Emmental cheese