Specimens of the uterine tube were obtained from ten healthy, ovario-hysterectomized cats. Ultrastructurally, a total of 66,000 cilia were examined. Atypical cilia were found in all examined subjects. The prevalence of compound cilia showed a range of 0.2% to 1.8%. Intracytoplasmic and swollen cilia ranged from 0.06% to 0.3% and from 0.03% to 0.3%, respectively. The microtubular pattern was examined in 7,000 cross-sectioned cilia and an abnormal pattern was found in 2.6%-6.5%. Abnormalities of peripheral microtubules were the prevailing defect. A central plug of electron-dense material was observed in 2-3% of the examined basal bodies. Several basal bodies characterized by an abnormal spatial configuration were also shown.