Several odour measurement methods were used during a 42-day test of commercial manure additives. Air samples were taken biweekly from the ventilated headspaces of 39 laboratory reactors containing swine manure. Ammonia and hydrogen sulfide was monitored continuously. A sensory panel evaluated odour concentrations in Tedlar bag samples using dynamic olfactometry. A gas chromatograph was used to analyse trace gases collected on adsorption traps. Odour concentrations ranged from 71 to 1426 OU/m3 (dilutions to threshold) and averaged 313 OU/m3. Mean hydrogen sulfide and ammonia concentrations were 475 ppb and 93 ppm, respectively. Six volatile fatty acids (acetic, butyric, isobutyric, isovaleric, propionic and valeric acids), and phenol, cresol, indole and skatole were the target compounds for trace gas analysis. Hydrogen sulfide, p-cresol and butyric acid had the highest correlation with odour concentration.