Air quality inside livestock buildings is known to have an impact on the health of workers as well as on the animal performance. This study evaluated the air quality inside milk-fed calf buildings during three seasons (winter, spring and summer). Measurements included concentrations and emissions of ammonia (NH3), hydrogen sulphide (H2S), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), as well as indoor temperature and relative humidity. NH3 was analyzed using nondispersive spectroscopy in the infrared; the H2S was analyzed by an electrochemical sensor, whereas the other gases (CO2, CH4 and N2O) were analyzed using gas chromatography. Results show that there are no important problems with the air quality in the milk-fed calf buildings evaluated. The indoor temperature was correctly controlled while the relative humidity was slightly higher than what is recommended in the literature. Ammonia was the only gas found at higher concentrations, but it remained generally under the time-weighted average (TWA) of 25 ppm, and always under the short-term exposure limit (STEL) of 35 ppm. A slight modification in the minimum ventilation setting would decrease both the ammonia concentration and the relative humidity of the air. [ABSTRACT FROM AUTHOR]