We used human respiratory epithelial cells in floating culture to study the motility and surface morphology of the cilia during ciliogenesis. Ciliary motility and surface morphology was examined by a high-speed video system and electron microscopy, respectively. On day 8 of floating culture, but rarely before, cells with numerous moving short cilia with mean ciliary beat frequency (CBF) of 17.8 +/- 2.5 Hz (mean +/- SD) were seen. The mean CBF was highest on day 10 (19.6 +/- 3.9 Hz) and reached 17.4 +/- 2.5 Hz on day 14. The ciliary beat amplitude (CBA) was recognized on day 8, abruptly increased on day 9, then continued with aging of the culture. The intracellular coordination of ciliary beats was poor on day 8 with random beat direction but improved up to day 12 when the intracellular uniform beat direction was established. However, intercellular coordination remained absent even on day 14. Results suggest that immature short cilia have a rigid beat pattern. With the elongation of the resulting whip-like movement, the ciliary beat was gradually synchronized. Although a ciliary elongation seems to be required for making intracellular coordination, other factors are involved in intercellular coordination. Also, a high CBF does not always indicate the activity of mature cilia.