Hyposmia is a fairly common complaint in patients with long-continuing aliergic or nonallergic rhinitis. Other factors such as aging, smoking, or nasal surgery may affect olfaction, but these have been little studied in rhinitisrelated hyposmia. The purpose of this study was to measure and compare olfactory thresholds in 105 rhinitis patients and 104 healthy controls and to analyze possible relationships between the sense of smell and rhinitis, age, sex, smoking, prick-test results, nasal resistance, and history of nasal or paranasal surgery. The olfactory threshold was assessed with a commercially available kit of squeeze-bottle pairs. The most important variables associated with the sense of smell were determined with stepwise multiple regression analysis, and intergroup differences were assessed with analysis of variance. The reference interval of olfactory thresholds by age was estimated with regression analysis. Nasal resistance was measured by active anterior rhinomanometry. Age and rhinitis were the only variables with significant effect on the olfactory threshold in the whole series. Both the proportion of hyposmic persons and the degree of the impairment of the sense of smell were significantly higher in the rhinitis group than in the control group. The nonallergic patients' sense of smell was poorer than that of seasonal or perennial allergic rhinitis patients. A history of operations for nasal polyposis was associated with hyposmia, but operations for chronic maxillary sinusitis were not. Neither smoking habits nor sex were related to olfactory thresholds. In conclusion, hyposmia in rhinitis patients is partly attributable to age-related changes, but our results indicate that the disease itself impairs the sense of smell.