Young's syndrome (obstructive azoospermia and chronic sinobronchial infection): a quantitative study of axonemal ultrastructure and function. The ultrastructure and function of nasal cilia and sperm tails were examined in 23 men with Young's syndrome and compared with data previously collected from 10 normal subjects. Quantitative electron microscopic assessment showed that sperm tails from patients with Young's syndrome contained significantly fewer central pair microtubules, radial spokes, and inner dynein arms, and their cilia contained less inner dynein arms than normal subjects. The Young's syndrome patients had normal in vitro ciliary beat frequency (11.4 +/- 0.9 Hz), and 12 of the 23 had normal nasal mucociliary clearance (15.0 +/- 5.0 minutes). However, the remaining 11 had markedly abnormal nasal mucociliary clearance in vivo. In these patients, the deficiency of ciliary inner dynein arms did not appear to affect ciliary function in vitro but may under mucus loading lead to abnormal in vivo ciliary function. The consistent abnormalities shown in cilia and sperm tails, though apparently minor, constitute a common factor in both the reproductive and respiratory tracts which may, in combination with abnormalities in the in vivo environment, lead to the features of Young's syndrome. 