A number of recent reports have demonstrated that long-term low-dose macrolide therapy is effective on in the treatment of chronic sinusitis as well as diffuse panbronchiolitis. In this study, we focused on the in vitro effects of macrolides on the ciliary beat frequency (CBF) of cultured human sinus epithelial cells. Sinus mucosal explants were successfully cultured on poly-L-lysine coated dishes with abundant outgrowthal ciliated cells. CBF measurements were carried out by a photoelectric method at specific predetermined sites on the 7 to 14 day cultured specimens. Both erythromycin (EM) and roxithromycin (RXM) had no significant effects on CBF at a relatively high concentrations (10^-4M). However, EM and RXM, at a concentration of 10^-5M, significantly increased CBF by 20% and 19% respectively four hours after administration. The cilio-stimulatory effects continued to the same degree for 24 hours. We further subdivided the ciliated cells into two groups on the basis of their mucociliary activity, predetermined before drug administration. The faster group included cells with a CBF of more than 630 beat/min and the slower group included those with a CBF of less than 630 beat/min. Interestingly, both EM and RXM at concentrations of 10^-4 M and 10^-5M showed no effect in the faster group. On the other hand, these drugs significantly increased the CBF of the ciliated cells in the slower group at both concentrations tested by a maximum of 34% with EM and 55% with RXM. These results suggest that macrolide antibiotics augment the ciliary clearance of human parnasal sinuses, and that this effect might be more pronounced when the epithelial ciliated cells are in somewhat disturbed conditions.