Objective To understand the modulating mechanisms in ciliary motility by NO signal pathway. Methods L arginine, the preferred substrate of NOS, was employed to act upon the cultured rat ciliated epithelia. After pre incubating with L NMMA, a NOS inhibitor, or ODQ,a sGC inhibitor, or Rp 8 Br cGMPS, an antagonist of PKG respectively, tissues were contacted with L arginine again. Ciliary beating frequency (CBF) was measured by phase contrast microscope and videotape analysis. Results L arginine increased CBF siginficantly. The effect of L arginine on CBF was blocked by L NMMA, ODQ or Rp 8 Br cGMPS.Conclusion L arginine may increase CBF via NO sGC cGMP PKG pathway.