Eight subjects scaled the overall perceived odor intensity of binary and ternary mixtures of the odorous substances pyridine, acetone, and ethyl acrylate. The results concerning basic principles of additivity for binary mixtures comply with those of earlier studies. For the ternary mixtures, the degree of arithmetic additivity in odor intensity seemed lower when a third component was added to a binary mixture than when the second component was added to a single odor, but this did not reach statistical significance. In general, the degree of arithmetic additivity inherent in the power function for single substances was found to be of the same size as the degree of additivity for binary as well as ternary mixtures. However, for binary mixtures, the additivity of the mixtures was found to approximate that of the substance with the lower exponent. In addition, the degree of additivity of the binary mixture was monotonically related to the average arithmetic additivity of the power functions for the two components.