Hydrogen sulphide (H2S) is a common toxic air pollutant and is emitted from decomposing manure at animal facilities. However, there have been only a few studies of H2S emissions from animal buildings, especially those involving long-term, high-frequency measurements. In the current study, H2S emissions from two, 1000-head pig-finishing buildings in Illinois, USA, were monitored with a high-frequency measurement system for 6 months in 1997 during two, partial, pig-growth cycles. Air sample streams were continuously taken from the pit headspace, and the pit and wall fan exhaust air. Hydrogen sulphide concentration was measured at each location with H2S converters and sulphur dioxide (SO2) analysers during 16 or 24 sampling cycles per day, resulting in 4544 sampling cycles and 219 days of reliable data. Building ventilation rate was the summation of pit fan and wall fan airflow rates. Airflow rates of the underfloor manure pit fans were measured directly with full-size impeller anemometers or calculated from airflow/voltage relationships of the fans. Airflow rates of the wall fans were calculated from fan operation and differential static pressure data and fan performance curves. Mean H2S emission was 0·59 kg/day per building, 0·74 g/day per m2 of pit surface area, or 6·3 g/day per animal unit (AU = 500 kg animal weight). The determination of H2S emission per AU was restricted to 193 days when building occupancy was at least 700 pigs per building. Higher temperatures and building ventilation rates resulted in significantly higher H2S emissions per AU.