A general equation set up for the study of transport properties has been applied to volatile organic compound (VOC) nasal pungency and eye irritation thresholds, as log (1/NPT) and log (1/EIT). The equation accounts for 93–95% of the total effect, thus suggesting that the main step is transport of the VOC from the gas phase to a receptor phase. In the case of odour thresholds the general equation accounts for only 77% of the total effect. A modified equation incorporates a factor for aliphatic aldehydes and carboxylic acids, and a general size effect that depends on the VOC maximum length. The size effect is important in that it leads to a cut-off effect that greatly reduces the potency of higher homologues. The various equations can all be used to predict chemosensory thresholds for thousands of VOCs.