The mucociliary transport of the human nasal mucosa was studied by using very small resin beads tagged with 51Cr. Several modifications of previous methods were introduced, e.g. kind of nuclide, particle size, pH, mode of application, measuring technique and reduction of local irradiation. Finally arrangements implying exact measurements of transport not only horizontally but also vertically or obliquely were obtained. No mucociliary transport was demonstrated in five of nine subjects with a common cold 10 days before or one week after the investigation. Xylometazolin as a nasal spray diminished the mucociliary transport significantly. In addition, the effects on mucociliary transport caused by homolateral or contralateral experimental nasal obstruction as well as by tobacco smoking were studied in healthy subjects. Finally, patients with various diseases: pollen allergy in free intervals, chronic rhinitis, septal deviation or perforation, and condition after laryngectomy were also investigated.