Mucociliary transport is a major defense mechanism of the airways. Mucociliary clearance is functionally and ultrastructurally organized at different levels from individual cilia to the ciliated tapestry. The correlations among ciliary beat frequency (CBF), secondary abnormalities (SCD), ciliary (dis)orientation (COR), coordinated ciliary activity and ciliary immotility were investigated based on the findings in over 700 non-PCD biopsies taken in the context of diagnostic investigations for respiratory problems. CBF decreased with increasing percentages of SCD, from 7.6 +/- 1.8 Hz (0-5% SCD) to 4.9 +/- 3.3 Hz (> 25% SCD). COR increased with increasing percentages of SCD, from 15 +/- 7 degrees for < 5% SCD to 28 +/- 8 degrees (> 25% SCD). SCD also correlated with ciliary (im)motility, but not with ciliary coordination. No correlation was found between COR and CBF. However, increased COR (28 +/- 8 degrees) was found in samples with only immotile cilia, compared to those with ciliary activity (19 +/- 9 degrees). Similar findings were demonstrated between COR and coordinated activity, particularly between immotile cilia (28 +/- 8 degrees) and those with coordinated ciliary activity (19 +/- 9 degrees). CBF values from samples with no coordinated activity (5.5 +/- 2.9 Hz) were significantly different from those with coordinated ciliary activity (7.4 +/- 1.6 Hz). In conclusion, mucociliary transport is a well organized, complex process with many interactions between parameters at various levels of functional and structural organization. SCD seems to play a crucial role. The correlations among the different parameters can help us further understand the functional and ultrastructural mechanisms needed for efficient mucociliary clearance.