The measurement of peak nasal inspiratory flow (PNIF) is a rapid, convenient, and objective way to assess nasal patency. It is used much less commonly, however, than Wright Peak Flow (WPF), in part, because of concerns about its reproducibility. In order to compare the reproducibility of PNIF with WPF, we obtained multiple measurements of both flows in each of ten healthy, nonsmoking, trained subjects five times throughout the same day and daily throughout the same week. Mean PNIFs (L/min) were 140 immediately after arising, 170 at breakfast time, 183 at lunch time, 170 at dinner time, and 161 at bedtime. Corresponding mean WPFs were 528, 528, 535, 535 and 531 L/min. Peak nasal inspiratory flow coefficients of variation representing minute to minute, hour to hour, and day to day variation were 9.8, 13.5, and 9.7, respectively. Corresponding coefficients of variation with WPF, 2.4, 1.9, and 2.3, were significantly lower. Variability of PNIF and WPF did not increase with increased time spans, suggesting that variation in airway size is less important than variation in technique. Responses to intranasal oxymetazoline, as determined by changes in PNIF and changes in subjective assessments of nasal patency, were then evaluated in ten patients with nasal obstruction. These persons noted a mean subjective improvement of 68% (P = .0002) and demonstrated a mean objective improvement of 21% (P = .05). Posttreatment PNIFs of many individuals who reported substantial subjective improvement failed to exceed the expected variability of the test. This experience fails to demonstrate the utility of PNIF determinations for routine clinical use.