Nasal reactivity to histamine was evaluated in 40 normal subjects. The application of a chloride histamine solution (1 mg) registered in 90% of the subjects the appearance of sneezing with the number of sneezes ranging between one and fourteen (5.7 +/- 3.76) and an average increase in the total resistence in the inspiration phase of 93.1% (+/- 63.2) and in the expiration phase of 98.1% (+/- 60.5) with a range between 37.7% and 24.1%. The authors conclude that sneezing and above all nasal congestion evaluated rhinomanometrically represent two important parameters in the evaluation of nasal reaction; an increase greater than or equal to 200% of the total nasal resistance can surely be considered an index of nasal hyperreactivity.