significantly different from the discrimination accuracy between two-component mixture and one component odorants (unpublished data). These results suggest that the concept of brown is also valid in olfaction. We continued to explore this assumption by generating mixtures of various components and comparing their similarity using Psychophysics tests. In the next step we compare the similarity results to the perceptual and chemical characters of their ingredients. ExperimentalOdorants: 80 odorants were diluted to equal intensity. Ten mixtures were made of 4, 15, 20, 25 and 30 components. There were two versions of each mixture; the odorants in each mixture were chosen randomly.Procedures: All experiments were conducted in rooms specially designed for olfaction experiments. These rooms are coated in stainless-steel to prevent odor adhesion. All interaction with subjects was by computer-generated digitized voice, and subjects provided their replies through a computer keyboard. In order to minimize the effect of olfactory adaptation, a 40 second inter-sample interval was maintained between mixture presentations. Psychophysics test: Five subjects participated in this study. The task was to rate the similarity between two mixtures in a range of 1 to 9. Each subject came twice, on successive days. On the first day, the comparison was between mixtures 4A, 15A, 15B, 20A, 20B, 25A, 30A and on the second day, the comparison was between the mixtures 4B, 15A, 15B, 20A, 20B, 25B, 30B, summing the total of 42 comparisons including repeated ones.Statistical Analysis: We used the Mann-Whitney U-test as well as a two-tailed T-test to discern whether or not data gathered from both the descriptor quality survey and comparison test was statistically significant. Although the Mann-Whitney U-test and two-tailed T-test are designed to measure the same basic idea, that is statistical significance, they have one fundamental difference; while a two-tailed T-test is applicable to parametric data, the Mann-Whitney U-test is applicable to non-parametric data as ours turned out to be. Physicochemical olfactory space: Each of the 12 odorants we used was described using 3224 chemical properties obtained using Dragon analytical chemistry software. These properties range from simple values such as molecular weight, number of atoms and bonds etc., and on to complex derived indices. These individual physiochemical measures were then Z-scored to allow for equal treatment.Perceptual space: Ten different subjects rated each mixture using 24 verbal descriptors that were chosen based on their STDEV of 144 odorants from 146 descriptors in Dravnieks' Atlas (1982). 10 subjects rated the applicability of each descriptor to the said mixtures on a scale from zero to five. A score of zero denotes that the descriptor is not present and a score of five denotes that the descriptor is highly appropriate to the odor evaluate. The rating of each descriptor for each odor was calculated by considering both the number of subjects that answered the rating question and the average rating they provided. This allowed us to generate a space with 146 descriptor-dimensions containing the 12 odorants we used.Two-dimensional perceptual space: In addition to representing each odorant with 24 descriptors, we also represented each odorant with only two descriptors, intensity and pleasantness, which subjects scored from