Variation in nasal patency can be studied by rhinomanometry as well as by nasal expiratory and inspiratory peak flow rate. The accuracy of 12 sets of peak flow meters was tested in a standardized way using a pump. Differences between flow meters were found. Consequently it is recommended for a patient to use the same flow meter throughout a study. Comparison between nasal expiratory and inspiratory peak flow was performed before and after provocation of 12 grass pollen-allergic patients. Inspiratory peak flow showed certain advantages compared with expiratory peak flow measurements. The results can best be expressed as the means rather than the top values of three consecutive registrations. Twelve healthy subjects were also tested with rhinomanometry, nasal expiratory and inspiratory peak flow before and after decongestion with nose spray. Comparisons among the three methods showed significant correlations.