A total of 331 different volatile organic compounds (VOCs) and fixed gases from swine facilities in North Carolina, USA, were identified by gas chromatography (GC) and mass spectrometry. Of these, 203 were found in air samples adsorbed onto Tenax(Reg.), 112 were found in air samples adsorbed onto cotton material, and 167 different compounds were identified in the lagoon samples. The compounds identified were diverse, and included many acids, alcohols, aldehydes, amides, amines, aromatics [aromatic compounds], esters, ethers, fixed gases, halogenated hydrocarbons, hydrocarbons, ketones, nitriles, other nitrogen-containing compounds, phenols, sulfur-containing compounds, steroids, and other compounds. The vast majority of these compounds were present at concentrations below published odour and irritation thresholds. Yet human assessments indicated that odours (and irritant sensations) in the immediate vicinity of the swine houses (and even at distances beyond 1000 ft) were strong. Comparison of the findings from chemical and human assessments points to the importance of the cumulative effects of hundreds of compounds in producing odour and irritation downwind of swine operations. Many GC peaks from the samples were too small to allow identification of the compounds, but their presence could also contribute significantly to odour and irritation. Several methodological difficulties were associated with the human odour assessments. Odorous air evaluated in the field was simultaneously collected in Tedlar (Reg.) bags for evaluation in the laboratory; however, intensity ratings in the field were higher than those in the laboratory. This was due to the fact that organic dust (dried faecal material and feed) adhered to Tedlar (Reg.) bags and the tubing of collection/delivery systems; therefore, only VOCs from the vapour phase (but not the dust) reached the nose of the panelists in sniffing air samples obtained in Tedlar (Reg.) bags. Future collection and measurement techniques need to be developed that can evaluate odours from dust and vapour phases simultaneously in the laboratory. Dispersion models also need to be developed that account accurately for odour intensities downwind of animal operations. Finally, safety standards for odour exposures need to be determined that consider the risk of simultaneous exposure to hundreds of low level compounds.