Objective To observe the effect of lipopolysaccharide（LPS） and interleukin-1β（IL-1β） on the expression of inducible nitric oxide synthase（iNOS） gene and nitric oxide（NO） in human periodontal ligament cells（hPDLCs）. Methods After stimulating hPDLCs by LPS and IL-1β, RT-PCR had been used to identify the expression of iNOS gene. The activity of iNOS in the culture was quantitated by enzyme-linked immune sorbent assay （ELISA）. And the level of NO was determined by nitrate reductase method. Results Slight amount of iNOS and NO had been detected in hPDLCs without sitimulation, but when stimulating with LPS and IL-1β, the amount of the iNOS mRNA increased significantly in the cells in the time and dose dependent way（P
