Three types of measurement were employed to assess the effects of aging on nasal irritation (common chemical sense). These were measurement of detection threshold of CO2 mixed with air, measurement of the threshold concentration of CO2 that causes a transient reflex apnea, and measurement of the suprathreshold perceived strength of five levels of CO2 by the method of magnitude matching. Ancillary measurements included nasal airflow resistance and magnitude matching of an odorant (1-butanol). Twenty elderly (67 to 93) and twenty young persons (19 to 31) served as subjects. The young and elderly gave no evidence of average difference in detection threshold. In contrast, the elderly group showed a strong elevation of the threshold of apnea and a marked weakening of perceived CO2 suprathreshold strength. CO2 and butanol approximated power functions of concentration level, functions for the elderly being depressed relative to those for the young. Although the elderly had on the average slightly higher nasal resistance than the young, the differences played at most a minor role in the perception of nasal stimuli.