Ciliary orientation was studied in 43 patients with the "immotile cilia" syndrome. Twenty-four of these patients had total situs inversus. One mucosal specimen was taken from uterine cervical epithelium, 2 were from bronchial mucosa and 40 from nasal mucosa. The orientation of the cilia was measured from micrographs using a semiautomatic image analyzer (IBAS I). The results from patients were compared with those of 10 control subjects. The mean standard deviation and its standard deviation of the angles of ciliary orientation was 39.7 degrees +/- 9.2 degrees in 43 patients and 27.4 degrees +/- 4.3 degrees in the control group. The difference between the groups is highly significant statistically (P less than or equal to 0.001). However, there were no statistically significant differences in the standard deviations of ciliary orientation between the fields sectioned near the cell membrane or near the ciliary tip. We were also unable to find any significant differences in the standard deviations of the ciliary angles in the specimens taken from brush biopsies and excisional biopsies. There were also no statistically significant differences between the standard deviations of the ciliary angles for the groups with or without situs inversus. If 35 degrees is considered to be the limit value for the mean standard deviation between normal and pathological specimens in our total material, this would give a specificity of 0.90 and a sensitivity of 0.72.