We describe how ciliary beat frequency (CBF) of human respiratory epitheliumin vitrocan be robustly and quickly measured. The proven photometric technique has been improved by using a microcomputer to calculate and display the results. The software, which runs on an IBM-compatible PC, was developed using Borland Turbo Pascal and employs a fast Fourier transform routine to derive the CBF. Results are displayed almost as soon as a cell is identified under the microscope, and are in accordance with previous work. The technique can now be used diagnostically and for a variety of drug trials on respiratory epithelium.