Investigation of the effect of environmental and pharmacological factors on human respiratory epithelium requires standardization of measuring conditions. Ciliary beat frequency (CBF) and its shift were determined photo-electrically in 43 biopsies of human nasal mucosa. Curette biopsies were compared to forceps biopsies. CBF variation between three different cells of one biopsy sample did not differ for the two biopsy techniques. The ciliated cells of forceps biopsy specimens showed a more constant beating pattern which resulted in a small CBF shift. It appeared that in studying ciliary activity a continuous layer of ciliated cells which is in contact with the basal membrane is required. Therefore forceps biopsies are preferable to curette biopsies. The environmental temperature has to remain constant since CBF is temperature dependent. The pH and osmolarity of the medium do not influence CBF when kept within a certain range. No effect of medium superfusion flow rate was seen.