It has been proposed that odorant suppression of the cyclic nucleotide-gated (CNG) channel is responsible for olfactory masking. In this study, the effect of odorant chain length and functional group on this suppression was investigated. Because similar suppression has been observed for voltage-gated channels also, we used voltage-gated Na channels in the olfactory receptor cell as a tool for substance screening. These features were then re-examined using CNG channels. Interestingly, both CNG and Na channels were suppressed in a similar manner-carboxylic acids had little effect and suppression became stronger when the chain length of the alcohol or ester was increased. Degree of suppression was correlated with the distribution coefficients (Log D), irrespective of the molecules used. Results obtained here may provide information for the development of novel masking agents based on molecular architecture.