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Seasonal temperature inside two gestation (dry) sow buildings monitored varied from near 20 0C in cold weather up to 25 0C in the summer. The inside summer temperatures were suppressed due to the presence of an evaporative cooling unit combined with the tunnel ventilation system. Diurnal temperature variations were relatively small during cold, mild, and warm condition but spatially warmer temperatures (up to 5 0C) were seen at the exhaust or fan end of the barns when the tunnel ventilation mode was operating. Seasonal variations in NH3 and H2S weekly average concentrations were from 2 to 25 ppm and 100 to 1000 ppb, respectively. These swings in concentrations were primarily the result of changes in the barn ventilation rates from winter to summer, since ventilation rates and gas concentrations are inversely related. Even though concentrations were seasonal, NH3 and H2S emission rates (product of ventilation rates and gas concentrations) were quite constant over the 15-month sampling period (Jacobson, et al. 2004). Diurnal gas concentrations for various temperatures do show variations especially during mild weather (cool nights and warm daytime temperatures). Results showed spikes of both NH3 and H2S concentrations that are probably explained from animal activity such as feeding and also removal of the liquid manure from shallow drain gutters. Finally, spatial variations of the gas concentrations exist in the barns primarily during the summer when the tunnel ventilation mode is operating and gas levels rise at the exhaust end of the buildings.