A reproducible technique, utilising a graphics tablet and a personal computer for measuring ciliary orientation from electron micrographs of ciliated epithelium, was assessed. Ciliary deviation was measured in 47 normal subjects (mean ciliary deviation +/- 1 SD was 14.6 (3.3 degrees)), in eight patients with bronchiectasis and normal ciliary function (15.1 (6.5 degrees], and in seven patients with primary ciliary dyskinesia (38.7 (7.8 degrees); significantly greater than the first two groups). Measurements of ciliary deviation at the tip, base, and basal feet showed very little variation along the ciliary shaft in all three groups, suggesting that valid measurements of ciliary deviation can be made at any level of the cilium. Mean ciliary deviation in normal subjects was always less than 30 degrees; all patients with a mean ciliary deviation of greater than 30 degrees had recurrent respiratory tract disease. Four of seven patients with primary ciliary dyskinesia had ciliary disorientation; in one this was the only defect. Measurements of inter- and intraobserver variability using this method showed a maximum difference between observations of 4.1 degrees. It is suggested that ciliary orientation should be measured in patients suspected of having defective ciliary function or structure, or both.