Using confocal laser scanning microscopy and MTT assay, the effects of Rhein on single cell i dynamics and TNFα production in normal and LPS-stimulated rat peritoneal macrophages (PMΦ)?were investigated. Rhein had not a disinct effect on TNFα production in normal PMΦ, but could obviously inhibit TNFα release in LPS-stimulated PMΦ in dose-dependent manner. 10-4 mol/L Rhein could inhibit the effect of LPS by 72%. Noticeably, Rhein not only lowered the rising of i in LPS-stimulated PMΦ, but also altered the dynamical mode of i, which means that Rhein could transform the 'plateau-shaped' peak of i into the oscillating mode. In the case of extracellular Ca2+-free, Rhein further transformed the i dynamics into a single peak of lower amplitude. These results indicate that Rhein reducing the increase in i is the key of signal transduction pathway that Rhein inhibited the TNFα production in LPS-stimulated PMΦ. It further suggests that inhibition and quasi-periodic modulation on influx of extracellular calcium as well as on intracellular calcium release in involve in the regulative mechanism of Rhein.