Hydrogen sulfide (H2S) concentration and emission at a modern mechanically ventilated swine finishing building with a deep pit were continuously measured for three summer months. The building is located near Bloomington, Illinois, USA. Ventilation rates, temperatures, and pig inventory in the building were also continuously measured or recorded. A total of 88 days of valid data were obtained between 26 June and 25 September, during which the average daily mean (ADM) ambient temperature was 21.8 degrees C. The test began with 887, 19-kg pigs in the building and ended with 874, 83-kg pigs. Hydrogen sulfide was measured with a sulfur dioxide (SO2) analyser equipped with a thermal oxidizer that converted H2S to SO2. Building ventilation rates were determined by continuously monitoring exhaust fan operation and differential static pressure. Daily mean building H2S concentrations ranged from 38 to 536 ppb. The ADM building concentration (average of three locations) was 173+or-21 ppb (mean+or-95% confidence interval). The maximum concentration, averaged over 7- or 12-minute sampling periods, was 1624 ppb. The 25th, 50th (median), and 75th percentile values were 413, 527, and 662 g/day for daily mean building H2S emission and 4.4, 5.8, and 12.4 g day-1 AU-1 (animal unit=500 kg live mass present in the building) for daily mean specific emission, respectively. These H2S emissions were much greater than emissions measured or estimated in previous studies. Based on daily means, H2S concentration was inversely proportional (P<0.05) to ventilation rate (r=-0.68), whereas building H2S emission was influenced somewhat (P<0.05) by building temperature (r=0.29) and ventilation rate (r=0.23).