This study is an attempt to establish the most suitable inert substance and normal parameters for nasal mucociliary transport time in normal adults: 79 subjects were taken into consideration, aged between 19 and 74 years, and were selected on the basis of negative outcome to anterior and posterior rhinoscopy , absence of any recent manifestation of rhinopharyngeal pathology and absence of allergy. The authors examined the possible modification of this particular index of nasal function in relation to the position of the head, when inclined or erect, to physical stress and to the hour at which the trials were carried out (9.30 a.m.-5.30 p.m.); they also carried out a statistical analysis of the results. For the study of the nasal mucociliary transport (MCT) time, an original composition of vegetable charcoal powder and saccharin powder at 3% is used. Vegetable charcoal powder was chosen because, not only it is non-toxic and easy to trace, but also because it is insoluble in water and therefore able to provide data on MCT time much nearer to that of effective MCT. Pure saccharin powder was added to the vegetable charcoal powder both in order to offer further data on a soluble substance as opposed to an insoluble one, and also because, as such, it interacts readily with the fluid which covers the mucus and provides an MCT time presumably nearer to that of clearance. From the statistical analysis of the data, it is possible to affirm that charcoal powder is the most suitable inert substance for the quantification of the parameter of 'normality'.