Studies on the irritative effects of acetone vapor in humans and experimental animals have revealed large differences in the lowest acetone concentration found to be irritative to the respiratory tract and eyes. This has brought on much confusion in the process of setting occupational exposure limits for acetone. A literature survey was carried out focusing on the differences in results between studies using subjective (neuro)behavioral methods (questionnaires) and studies using objective measurements to detect odor and irritation thresholds. A critical review of published studies revealed that the odor detection threshold of acetone ranges from about 20 to about 400 ppm. Loss of sensitivity due to adaptation and/or habituation to acetone odor may occur, as was shown in studies comparing workers previously exposed to acetone with previously unexposed subjects. It further appeared that the sensory irritation threshold of acetone lies between 10,000 and 40,000 ppm. Thus, the threshold for sensory irritation is much higher than the odor detection limit, a conclusion that is supported by observations in anosmics, showing a ten times higher irritation threshold level than the odor threshold found in normosmics. The two-times higher sensory irritation threshold observed in acetone-exposed workers compared with previously nonexposed controls can apart from adaptation be ascribed to habituation. An evaluation of studies on subjectively reported irritation at acetone concentrations < 1000 ppm shows that perception of odor intensity, information bias, and exposure history (i.e., habituation) are confounding factors in the reporting of irritation thresholds and health symptoms. In conclusion, subjective measures alone are inappropriate for establishing sensory irritation effects and sensory irritation threshold levels of odorants such as acetone. Clearly, the sensory irritation threshold of acetone should be based on objective measurements.