The 0-5 organoleptic scale is used widely in breath research and in trials to measure the efficacy of anti-odor agents. However, the precise relationship between odor scores and gas concentrations of target odorants is unknown. The purpose of this study was to relate mean organoleptic scores from odor judges (n = 7) for pure odorants (n = 8) representative of those found in oral malodor. Judges used a common 0-5 scale to report the odor intensity of sample sets in random order of concentration. Regression analysis of data showed that odor score was proportional to the log concentration of odorant, and comparison of slopes showed H(2)S to be the most significant in terms of odor power. Detection thresholds (mol.dm(-3)) were: Skatole (7.2 x 10(-13)) < methylmercaptan (1.0 x 10(-11)) < trimethylamine (1.8 x 10(-11)) < isovalerate (1.8 x 10(-11)) < butyrate (2.3 x 10(-10)) < hydrogen sulphide (6.4 x 10(-10)) < putrescine (9.1 x 10(-10)) < dimethyl disulphide (5.9 x 10(-8)). The study demonstrates the exponential nature of the olfactory response and shows that any single compound's contribution to malodor depends on odor power and threshold in addition to concentration.