The cyanide-metabolizing enzyme rhodanese is present in rat nasal epithelium at high activity levels. Cyanide is a common environmental pollutant. It is both toxic and an odorant. The high rhodanese activity in rat nasal epithelium may provide a mechanism for detoxicating inhaled hydrogen cyanide and may also play a role in olfaction by limiting the concentrations of cyanide in the nasal epithelium. The objective of this study was to determine whether high levels of rhodanese activity are also present in human nasal epithelium. On a per milligram mitochondrial protein basis, the rhodanese in human nasal tissue exhibited both a lower affinity (higher Km) for cyanide and a lower maximum velocity (Vmax) for cyanide metabolism than did rhodanese from rat nasal tissue. As in human liver, the human nasal enzyme appeared to exhibit substrate activation by cyanide. Rhodanese activity in the maxilloturbinates of nonsmokers was statistically higher than in smokers although only three samples per group were available. The Vmax/Km ratios for rhodanese from the nasal tissue of nonsmokers were consistently greater, thus suggesting the possibility of higher rates of cyanide metabolism in nonsmokers than in smokers.